Difference between revisions of "Paper - Comparative studies on the growth of the cerebral cortex 8 (1918)"

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^ For more extensive bibliographies see Huber ('99, '13) and Ranson (this number of this Journal).
 
^ For more extensive bibliographies see Huber ('99, '13) and Ranson (this number of this Journal).
 
 
 
==AUTHOR 3 ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, MAY 11==
 
 
 
 
THE THORACIC TRUNCUS SYMPATHICUS, RAMI
 
 
COMMUNICANTES AND SPLANCHNIC NERVES
 
 
IN THE CAT
 
 
S. W. RANSON AND P. R. BILLINGSLEY
 
 
From the Anatomical Laboratory of the Northwestern University Medical School^
 
 
NINE FIGURES
 
 
In other papers of this series, which appear on the preceding pages, we have dealt with the cervical portion of the sympathetic trunk, the superior cervical ganglion, and the branches which it gives off. We come now to a consideration of the thoracic portion, its rami communicantes and the splanchnic nerves. Our preparations were obtained from cats because most of Langley's observations were made on these animals and we wished to compare our results with his.
 
 
The work was started with the hope of throwing some light on the origin of the various types of fibers in the splanchnic nerves. Since these fibers are known to belong for the most part to segments caudad to the fifth thoracic, we began by studying the rami from the sixth to the thirteenth thoracic nerves and the corresponding portions of the trunk. It was only after the study of this material had shown that many significant details concerning this nerve trunk had never been described that we began the study of it in the first five thoracic segments. Hence the material representing this part was taken from different cats than those in which the sixth to the thirteenth thoracic segments were studied. But in each case a sufficient number of specimens was secured to make sure that the peculiarities encountered at different levels were characteristic for those levels. In all nearly twenty cats were used, exclusive of those on which operations were performed to produce the degenerations to be reported in the following paper.
 
 
1 Contribution No. 58, February 15, 1918.
 
 
405
 
 
 
 
406 S. W. RANSON AND P. R. BILLINGSLE^
 
 
About half of the material was fixed in osmic acid and the remainder in ammoniated absolute alcohol for the pyridine silver stain. The rami communicantes are so small and short that pyridine silver preparations were made in only a few instances, so that our observations on these are based chiefly on osmic acid preparations. For the rest of the work abundant material was available in which to compare the myelin sheath and axon content of the various parts of the sympathetic trunk and the splanchnic nerve.
 
 
When small nerves are subjected to the action of the silver and pyrogallic acid a diffuse precipitate forms throughout the specimen which renders it useless for microscopic study. In order to do away with this it is only necessary to subject large blocks of tissue to the action of the reagents. This can best be accomplished by imbedding the nerve in the spinal cord. The small nerve to be studied is dissected free and a fine silk thread is tied at either end of the stretch to be removed. With the aid of a long straight slender needle the thread attached to the end of the nerve is drawn through a piece of spinal cord and the nerve drawn in after it. The spinal cord should be prepared before the nerve is dissected out. The cervical portion of the cat's cord freed from dura and split in the m.edian sagittal plane into two lateral halves makes satisfactory blocks. Each lateral half is then cut into segments a little longer than the pieces of nerve to be removed. During these manipulations the nerve and cord should be protected from drying by the use of normal salt solution. In drawing the nerve into the cord the needle is run longitudinally through the anterior gray column and the thread pulled through until the nerve lies imbedded in the cord. The segment of the cord is then laid with its lateral convex surface upon a glass cover-slip and the silk threads attached to either end of the nerve are tied over the cover-slip so as to put gentle traction on the nerve. After two hours in ammoniated alcohol the silk thread can be cut off near the cord, which is then removed from the cover-slip and pared down with a razor until it forms a bar, the cross-section of which is not more than 4 mm. square. This should consist chiefly of the anterior gray column in which the nerve lies imbedded.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 407
 
 
ANATOMY
 
 
Truncus sympathicus. In the cat the thoracic portion of the sympathetic trunk presents an arrangement of its gangha and branches somewhat different from that found in man. The chief differences are in the fusion of the upper thoracic gangha to form the ganghon stellatum and in the mode of origin of the splanchnic nerves. The trunk hes along the sides of the bodies of the vertebrae ventral to the heads of the ribs, and consists of a series of ganglia, for the most part segmentally arranged, bound together by a continuous nerve cord. Each spinal nerve is connected with an adjacent ganglion by a gray ramus. A ganglion may send a gray ramus to two or more nerves, in which case it represents a combination of two or more segmental ganglia. Some compound ganglia are constant in their occurrence, as in the case of the stellate and the superior cervical ganglia; others may occur occasionally in any part of the trunk due to the fusion of two segmental ganglia. Thus the segmental character of the truncus is indicated by the gray rami, although in some cases adjacent segments may be fused. The white rami are much more irregular in their distribution. From all this it will be apparent that the best method of designating the ganglia is by giving: them the number of the spinal nerve to which they are connected by their gray ramus. The facts concerning the connections of the fibers of the gray and white rami, which will be detailed later in this paper, also bear out this conclusion. Langley ('91 a) has made use of the same method of designating the ganglia. When we speak of the twelfth thoracic ganglion we shall have in mind the ganglion whose gray ramus runs to the twelfth thoracic nerve, although a glance at figure 1 will show that there are less than twelve separate ganglia in the thoracic region, and that this particular ganglion usually receives a white ramus from the eleventh thoracic nerve. The portion of the continuous nerve cord which joins two successive ganglia together we shall speak of as an internodal segment and shall number the successive segments to correspond to the numbers of the ganglia below which they lie.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 409
 
 
The ganglion stellatum lies ventral to the first intercostal space and the angle of the second rib. It receives the gray and white rami from the first three thoracic nerves and sometimes from the fourth also. In addition it gives off a gray nerve, the ramus vertebralis, which follows the vertebral artery and gives off branches to the lower cervical nerves. According to Langley ('94), it can be traced in the cat as high as the third cervical nerve. The gray ramus to the eighth cervical nerve may run by itself. From its connection with the spinal nerves it is obvious that the stellate ganglion represents a fusion of elements which in man are found in the middle and inferior cervical and the first three (and sometimes four) thoracic ganglia. Beginning with the fourth or fifth thoracic segment, the ganglia are more regularly arranged. But sometimes a ganglion from which a gray ramus arises may be very small, and occasionally scattered ganglion cells or even fairly large ganglionic masses are found in the internodal segments.
 
 
Rami co7nmunicantes. While there is a gray ramus for each spinal nerve the white rami have a more limited distribution, Gaskell ('86) thought that in the dog they w^ere associated with the second thoracic to the second lumbar nerves only. But Langley ('92 a) has shown that in the dog, cat, and rabbit, white rami run from the first thoracic to the fourth lumbar nerves inclusive. Miller ('09) has shown that in man, contrary to the usual statement, the third and fourth lumbar nerves possess white rami. The rami communicantes of the first two thoracic nerves in the cat run directly to the stellate ganglion, those of the third usually join the trunk a short distance below and ascend in a common sheath with the trunk to reach this ganglion. The gray and white rami of the upper two or three thoracic nerves are commonly fused together, forming one mixed ramus for each of these nerves. From the fourth to the eighth spinal nerve the
 
 
Fig. 1 Diagram of the thoracic portion of the sympathetic trunk in the cat. Any branches which may run to the pulmonary or aortic plexuses are usually so fine as to escape notice in a careful dissection carried out with the aid of binocular lenses of X 2 magnification. In one case we found a branch from the sixth thoracic ganglion to the pulmonary plexus and one from the tenth to the aorta.
 
 
 
 
410 S. W. RANSON AND P. R. BILLINGSLEY
 
 
gray and white rami run close together and join the trunk at the level of the corresponding ganglion. From the level of the ninth or tenth thoracic nerve to the fourth lumbar the white rami are directed caudad and reach the truncus below the level of the ganglion to which the corresponding gray rami run, often at the level of the next ganglion below. In some cases a nerve may give off, in addition to this descending white ramus, a direct one which accompanies the gray ramus to the segmental ganglion.
 
 
A nerve may be connected with the corresponding ganglion by more than one gray ramus or a nerve may receive gray rami from two successive ganglia. This is particularly likely to be the case in the lower thoracic and lumbar regions where, in addition to the gray ramus from its own segmental ganglion, a nerve may receive a bundle of unmyelinated fibers from the next more caudal ganglion, which bundle accompanies the descending white ramus of the nerve. Langley ('94) has shown that 'Svhen the white ramus runs downward to a ganglion, as occurs from the ninth or tenth thoracic to the fourth or fifth lumbar nerves, the ganglion may supply pilomotor fibers to the two nerve areas, thus the fourth lumbar ganglion sends fibers to the fourth lumbar nerve by its gray ramus, and may also send fibers to the third lumbar nerve by the white ramus of this nerve."
 
 
Gaskell ('86) has shown that when a gray ramus is followed toward its corresponding spinal nerve it can usually be seen to give off branches which ramify in the connective tissue overlying the vertebrae. On these branches accessory ganglia may sometimes be found. In some cases the gray ramus could be seen to divide on reaching the spinal nerve, part of the fibers passing centrally, the rest peripherally.
 
 
The splanchnic rierves. In the cat the splanchnic fibers leave the sympathetic trunk in a series of six to ten small nerves. The first of this series is the largest and corresponds to the greater splanchnic nerve in man. The level of the trunk at which this nerve is given off varies. In a total of seventeen dissections it took origin from the thirteenth thoracic ganglion in six cases, from the thirteenth internodal segment in three, from the first, lumbar ganglion in four, from the first lumbar internodal
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 411
 
 
segment in three and from the second lumbar ganghon in one. Since it is well known that fibers of the splanchnic nerve come from segments as high as the fifth and sixth thoracic, it is obvious that these fibers must have descended in the sympathetic trunk to the point of origin of the splanchnic nerve. In man these same fibers leave the trunk in small bundles from the level of the fifth or sixth thoracic ganglia downward to the ninth, and these bundles are then gathered together to form the greater splanchnic nerve. In the cat other splanchnic nerves are given off somewhat irregularly from the upper five lumbar ganglia and internodal segments.
 
 
The thoracic rami co7nmunicantes. It is not necessary to review the early literature dealing with the rami communicantes, since the work of Gaskell ('86) may be regarded as the starting point of modern investigations on this subject. He made a careful histological examination of the spinal nerves and rami communicantes. The gray rami were found to be composed chiefly of unmyelinated and the white rami chiefly of myelinated fibers. In the roots of the spinal nerves only myelinated fibers were found. He argued that, since he found only myelinated fibers in the roots of the spinal nerves as they left the spinal cord, the only connection between the spinal cord and sympathetic trunk must be by way of the myelinated white rami, and that through them occurred the only possible outflow of visceral efferent fibers from the spinal cord. The ventral roots of those spinal nerves which he found associated with white rami, the second thoracic to the second lumbar inclusive, were seen to contain large numbers of fine myelinated fibers like those in the white rami, while the ventral roots of the other spinal nerves contained very few such fibers. These he regarded as visceral efferent fibers. A gray ramus was found associated with each spinal nerve. On reaching the nerve such a ramus was seen to divide, one part passing centrally, the other peripherally. Most of the unmyelinated fibers which ran centrally were seen to pass into the sheath of the nerve and become lost in the dense layers of connective tissue within the intervertebral foramen. Since no unmyelinated fibers could be found in the ventral roots nor in the dorsal
 
 
 
 
412 S. W. RANSON AND P. R. BILLINGSLEY
 
 
roots proximal to the spinal ganglion, Gaskell asserted that no non-medullated nerves leave the central nervous system either in the posterior or in the anterior roots, any such nerves being in reality peripheral nerves for the supply of the spinal membranes." This was the status of the question when Langley began his work. In 1892 he said:
 
 
It may be regarded as shown that only medullated fibers run from the spinal cord to the sympathetic chain, and that the white rami contain very many medullated fibers whilst the gray rami contain very few. The asserted sharp distinction between white and gray rami stands, however, on a different footing. So far as concerns their histological characters the difference between them is rather one of degree than of kind, they both contain medullated fibers of various sizes, and nonmedullated fibers.
 
 
On such evidence alone it could not be confidently asserted that no preganglionic fibers left the cerebrospinal nervous system by way of the gray rami. This question could best be attacked by physiological methods, i.e., by stimulating the spinal nerves within the spinal canal. Langley ('92 a) showed that, while stimulation of the nerves which were associated with white rami gave rise to responses in smooth muscles and glands, stimulation of those which possessed only gray rami produced no noticeable effect on these structures. He concluded that the myelinated fibers in the gray rami were either not preganglionic efferent fibers or were too few to produce any perceptible effect.
 
 
Most of Langley's histological observations were made on teased nerves, and it has seemed worth while in connection with the general review of the entire sympathetic nervous system which is being made in this laboratory to check up his histological observations by a careful examination of the rami communicantes of all the spinal nerves in sections stained with osmic acid. In this paper the rami of only the cervical and thoracic nerves are considered.
 
 
White rami communicantes. The course of the white rami within the sympathetic trunk will be taken up in connection with that nerve cord. Our present concern is with the character of the fibers. The white rami are not always pure, but are often accompanied by one or more fascicles of unmyelinated fibers
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 413
 
 
having all the characteristics of small gray rami. Such fascicles are, however, always sharply defined and do not form a part of the white ramus proper. These composite rami are especially frequent in the upper thoracic region where the gray and white rami are regularly fused. The first two or three thoracic nerves usually have each a single mixed ramus. Mixed rami are also not uncommon in the lower thoracic and upper lumbar regions where the white ramus runs downward.
 
 
Osmic acid preparations of the white rami of the cat show that these contain great numbers of small myelinated fibers with which are mingled some larger fibers varying in number in the different rami. In the dog Gaskell found that the small fibers measured 1.8 to 3.6^1. He believed that all visceral efferent fibers were of this size. Langley ('96 a) states that:
 
 
In the cat, the medullated fibers of the sympathetic appear to be somewhat smaller than in the dog. In the dog, I found that most of the nerve fibers could be classed as belonging to one of three types, viz., large fibers about 8 m in diameter, medium fibers about 5 /x in diameter, and small fibers about 3 fx in diameter, though all sizes from 2 to 12 m were present. In the cat the corresponding fibers are about 7 /j., 4.5 fj. and 2.5 fx; fibers from 2 to 10 ju and occasionally of greater diameter than 10 fx being present.
 
 
Our measurements of the medullated fibers in the white rami of the cat show that the small fibers vary in diameter from 1.5 to 3.5m. Between these two extremes there are fibers of all sizes and in about equal proportion. There are also fibers of larger size, but in much smaller proportion. The second thoracic white ramus contains, however, a great many fibers measuring 4.5/x or 5m, as will be seen in figure 2. The larger fibers, which vary in size from 5 to 13^ are not evenly distributed in the white rami and will be considered more in detail when some of the individual rami are taken up.
 
 
There does not seem to be any reason for grouping the fibers into three classes as Langley has done. There w^ould be more reason for making two groups: one less than 4.5m, the other larger. It is probable that nearly all of the preganglionic efferent fibers would fall in the first group, but this group would also contain, as we shall see, some of the smaller sensory fibers. The
 
 
 
 
414 S. W. RANSON AND P. R. BILLINGSLEY
 
 
second group would include the large and medium-sized sensory fibers.
 
 
Are there unmyelinated axons scattered among the myelinated fibers of the white rami? We must exclude from consider&,tion
 
 
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Fig. 2 Second thoracic ramus cominunicans in the cat consisting of two fascicles, the larger representing the white and the smaller the gray ramus. Osmic acid. X 425.
 
 
here the bundles of unmyelinated fibers which run as definite fascicles and represent small gray rami included in the white. Gaskell ('86) found unmyelinated fibers in the white rami and said that there is strong evidence that they arise from the
 
 
 
 
THOKACIC TRUNCUS SYMPATHICUS 415
 
 
posterior root ganglia." It is clear from the context that he believed the spinal ganglia contained autonomic cells and that the unmyelinated fibers running from these ganglia by way of the white rami were of the same nature as the unmyelinated fibers arising from sympathetic ganglia.
 
 
We have pyridine silver preparations of the tenth, eleventh, and twelfth white rami from one cat. While these are not altogether satisfactory, it is possible to see that they contain a considerable number of unmyelinated fibers. In the paper which follows we shall present evidence to show that these fibers arise in the spinal ganglia, but we believe that they are to be interpreted as afferent, not as postganglionic efferent fibers. If they belonged to the latter category it would be hard to account for the negative results of stimulating the splanchnic nerves after injection of nicotin (p. 436).
 
 
There has been some difference of opinion concerning the rami of the first thoracic nerve. Gaskell ('86) found only a gray ramus connected with this nerve in the dog. Edgeworth ('92) found that this ramus in the dog contained unmyelinated, large myelinated, and a few fine myelinated fibers. From this account we would conclude that there was no clear separation of the fibers into fascicles representing gray and white rami. Langley ('92 a) studied the rami of the first thoracic nerve in the cat, dog, and rabbit, and in every case found the highest white ramus coming from the first thoracic nerve. In the cat we find the gray and white rami of the first thoracic nerve united in a mixed ramus in which they appear as separate fascicles. The white fascicle contains a rather large number of fibers over 6/x. It is particularly in the number of these large fibers that the white rami differ from one another. In individual white rami the content of large fibers was found as follows:
 
 
First thoracic white ramus, 40 fibers over 6^ in diameter, one of which was much larger than the others and measured 13/1.
 
 
Second thoracic white ramus, 17 fibers Qfx in diameter or larger. Of these 5 measured 13^. There were also a rather large number of fibers from 4 to 6/i in diameter.
 
 
 
 
416 S. W. RANSON AND P. R. BILLINGSLEY
 
 
Third thoracic white ramus, 23 fibers 6yu in diameter or larger. There were no very large fibers like those in the two preceding rami.
 
 
Fourth thoracic white ramus, 10 fibers 6^ in diameter or greater. No very large fibers.
 
 
Fifth thoracic white ramus, 24 fibers 6yu in diameter or greater, of these 2 measured 13yu.
 
 
Sixth thoracic white ramus, 73 fibers G/x in diameter or greater, the largest of which measured 10/x.
 
 
Seventh thoracic white ramus, 109 fibers 6/x in diameter or larger. There were no fibers of 10 to 13/x diameter.
 
 
Eighth thoracic white ramus, 101 fibers 6^ in diameter or greater. None of them very large fibers.
 
 
Ninth white ramus, contained 174 large fibers, but many of them were a little under 6^ in diameter.
 
 
Tenth white ramus. In this specimen we found a direct ramus to the tenth thoracic ganglion and a descending ramus to the eleventh. The direct white ramus contained 130 large fibers, one of which measured 10^; the descending white ramus in this case consisted very largely of fibers 6 to S/j. in diameter, 106 in number. The total number of large fibers coming from the tenth thoracic nerve was thus 236.
 
 
Eleventh thoracic white ramus. Here again we found a direct and a descending white ramus and in both together there were 59 large fibers.
 
 
Twelfth thoracic white ramus, 11 large myelinated fibers, of which the largest was 8^ Thirteenth thoracic white ramus, 56 large myelinated fibers.
 
 
While these white rami did not all come from a single animal — the first was from one cat, the second to the fifth from another, and the sixth to the thirteenth from a third cat — the results have been checked on a sufficient number of other cats to show that the larger differences between the rami of the several levels are significant. The greatest outflow of large fibers occurs through the seventh to the tenth or eleventh white rami, inclusive. Figure 3 shows the relatively large number of them in the tenth.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS
 
 
 
 
417
 
 
 
 
There seems also to be a rather large number in the first thoracic ramus. The upper two thoracic rami^ are also characterized by the presence of fibers as large as 13//, which are usuallyabsent from the others.
 
 
 
 
 
 
 
 
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Fig. 3 Tenth thoracic white ramus of the cat with associated gray fascicles. There was a large separate gray ramus not shown in the figure. Osmic acid. X425.
 
 
Bidder and Volkman ('42) were the first to consider these larger fibers as sensory. Langley ('92 a) found difficulty in correlating the degree of sensitiveness of different parts of the sympathetic system, as evidenced by the ease with which their stimulation would produce general reflexes, with the number of
 
 
 
 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 4
 
 
 
 
418 S.' W. RANSON AND P. R. BILLINGSLEY
 
 
large myelinated fibers they contained. He suggested the possibility that many of the larger fibers mediate some special sense or subserve special visceral reflexes. Many of them can be traced to the Pacinian corpuscles (Langley, '00). Edgeworth ('92) devoted special attention to the '4arge-fibered sensory supply of the thoracic and abdominal viscera" in the dog. According to him,
 
 
It was found that the large medullated sympathetic fibers exist in the rami communicantes of the nerves from the first dorsal to the third lumbar inclusive; none were found in the rami aboral to this. The large sympathetic fibers are found scattered among the other fibers in the nerve bundles forming the ramus, and not grouped together or isolated by any septa from the other fibers. In the uppermost dorsal rami the large sympathetic fibers are fairly plentiful, in the upper and middorsal rami they are somewhat fewer in number, whilst in the lower dorsal rami a sudden large increase takes place, which continues as far as the second lumbar ramus where the outflow practically ceases. A few however are constantly to be found in the third lumbar ramus — whilst below this as stated above none are seen.
 
 
Edgeworth included among the large fibers those measuring 7.2 to 9/x and ignored the even larger number of fibers measuring less than 7^ but still distinctly larger than preganglionic fibers, so that his results are only in a general way comparable to ours. He states that the large fibers are as numerous in the gray as in the white rami. In the cat, as we shall see, they are usually not present in the gray rami of the cervical and thoracic regions. Langley ('92), working with the cat, found some large fibers, 7.2 M or upwards, in the gray rami of the low^er cervical nerves; in the white and in the gray ramus of the fourth lumbar nerve, and in the gray rami of the fifth, sixth, and seventh lumbar nerves. These were not numerous, but with them were a considerable number of fibers about 5m in diameter.
 
 
It has been assumed that all the large myelinated fibers are afferent, but are all the visceral afferent fibers large? Added precision could be given to this question of the myelinated visceral afferent fibers by the study of the white rami after degeneration of the preganglionic fibers resulting from section of the corresponding spinal nerve roots proximal to the spinal ganglia. We have examined the white rami of the ninth, tenth, and elev
 
 
 
THORACIC TRUNCUS SYMPATHICU3 419
 
 
enth thoracic nerves after all the preganglionic fibers had been eliminated. As is shown in the figure on page 444 of the eleventh thoracic white ramus, the majority of the fine myelinated fibers have degenerated, but a considerable number of all sizes remain. In this particular case the small and medium-sized fibers are more numerous than the large ones. In some other degenerated white rami the large ones are relatively more numerous. On the whole, the sensory fibers of the white rami may be said to be of all sizes from 1.5 to 8 or lO^t, no one size greatly predominating over the others. In some rami as in the upper thoracic larger fibers up to 13^ may be present.
 
 
These sensory myelinated fibers which are found in the white rami after section of the corresponding nerve roots proximal to the spinal ganglia take their origin from nerve cells in these ganglia. In the second paper of this series we have shown that there was no reason for assuming that there were sensory cells in the sympathetic ganglia which sent their axons into the dorsal roots or spinal ganglia (p. 333). Langley has shown that
 
 
Section of the inferior splanchnics, the lower lumbar sympathetic chain, or of a white ramus does not as a rule cause degeneration of any mediillated fibers in the central ends of the nerves. Sometimes a few degenerated fibers may be followed for a short distance, but these appear to belong to small gray bundles and to pass off to peripheral tissues.
 
 
When we come to the study of the sympathetic trunk we shall find that while some of the fibers of a white ramus end in the nearest ganglion, a larger proportion of the fibers run up or down in the trunk for longer or shorter distances. That is to say, a white ramus is in no special sense associated with its own segmental ganglion. The gray rami, on the other hand, are in a very special sense the branches of the corresponding ganglia.
 
 
Gray rami comniunicantes. The physiological experiments of Langley ('91 a, '94) on pilomotor, vasomotor, and secretory fibers show that the majority of these postganglionic fibers take origin from the cells of that ganglion to which the gray ramus is attached, but in some cases a minority of the fibers are connected with cells in an immediately adjoining ganglion. On the histological side this arrangement is indicated bj^ the fact
 
 
 
 
420 S. W. RANSON AND P. R. BILLINGSLEY
 
 
that a gray ramus plunges directly into a ganglion, its fibers being lost in the fiber complex; while in the case of the white rami it is easy to see that a large part of the fibers do not enter the ganglion, but pass along its surface to join the trunk above or below.
 
 
While the gray rami are composed in by far the greater part of unmyelinated fibers, each contains at least a few myelinated fibers and some contain a very considerable number, Langley ('96 a) has shown that the number of such fibers has been greatly underestimated. The seventh lumbar grsiy ramus of the cat may contain more than 300. According to Edgeworth ('92), the branches from the stellate ganglion to the cervical nerves in the dog contain a few small myelinated fibers, but no large ones. In conmaenting on Edgeworth's paper Langley ('92) states that he has always found some large myelinated fibers in the gray rami of the lower cervical and fourth, fifth, sixth, and seventh lumbar nerves. The number of small myelinated fibers is in general proportional to the size of the gray ramus, i.e., to the number of unmyelinated fibers it contains (Langley, '96 a). He states that the myelinated fibers range in size from L8 to 10/x and the variation in number affects almost entirely the small ones, the most constant form being the fiber of medium caliber. The number of myelinated fibers varies considerably in different mammals, there being many more in the cat than in the rabbit (Langley, '00). Miiller ('09) demonstrated the presence of myelinated fibers in the gray rami of man.
 
 
In the rami to the first three cervical nerves from the superior cervical ganglion we found that the number of myelinated fibers varied greatly in different specimens. Most of these fibers were less than 3.3yu in diameter, although occasionally larger fibers up to 6 or 7n were found, also in one case a single fiber measuring 10 fx. We have examined sections of the ramus vertebralis of the stellate ganglion in one cat and found that it contained about the same proportion of myelinated fibers as the other gray rami. There were no fibers as large as 6^. All of the thoracic gray rami contain a few myelinated fibers. These are for the most part small, but a few large fibers were found in the upper thoracic gray rami. We cite some enumerations which may be regarded
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 421
 
 
as typical. In "one cat the sixth thoracic gray ramus contained one myeUnated fiber 6.6ai in diameter and three others much smaller. The seventh was fused with the white ramus, and it was difficult to be sure which myelinated fibers belong to it. The eighth contained 3, the ninth 20, the tenth 27, the eleventh 14, the twelfth 6, and the thirteenth 16, all under 4^ in diameter.
 
 
What is the function of these myelinated fibers and from what cells do they arise? Many are postganglionic fibers arising from the cells of the ganglia of the sympathetic trunk. The observations to be found in the literature showing that postganglionic fibers in some instances acquire myelin sheaths have been given qn page 323. As already mentioned, Gaskell showed that as a gray ramus reaches its spinal nerve it divides into two fascicles, one of which is directed peripherally. This peripheral branch receives its share of the myelinated fibers. These being directed toward the periphery can scarcely be other than postganglionic fibers. It is reasonable to suppose that many of those which turn centrally are of the same nature (Langley, '92 a).
 
 
In 1896 Langley made a careful study of this problem. After a variety of experimental lesions involving degeneration of fibers of Various origin in different experiments, he counted and measured the normal and degenerated fibers in the gray rami of the lumbar and cervical nerves. We quote his conclusions:
 
 
The great majority of these (myelinated) fibers arise from sympathetic nerve cells in the corresponding sympathetic ganglion. In some cases, but not always, a few arise from sympathetic cells in an adjoining ganglion. No efferent fibers run from the spinal cord to the S3'mpathetic by way of the gray rami. In some cases, but not commonly, a few efferent medullated fibers, passing to the sympathetic by the white rami, leave the sympathetic bj^ the gray rami. These are to be considered as fibers on their way to aberrant sympathetic nerve cells lying in the gray rami before they reach the spinal nerves. The afferent medullated fibers of the gray rami are of various sizes, 2/x, 4^*, 6m, and in some cases 8 to 12/i. These are few in number and rapidly diminish (especially those of more than 4/x in diameter) in passing from the lower lumbar to the coccygeal rami. Most of (these) afferent fibers join the sympathetic by white rami (only to leave again by the gray), but there is some evidence that a few, especialh^ the larger ones may run to the sympathetic by the gray rami.
 
 
 
 
422 S. W. RANSON AND P. R. BILLINGSLEY
 
 
In spite of the presence of a few myelinated sensory fibers in the gray rami no refiex of any kind has been obtained by stimulating them" (Langlej^, '00). This may be due to their small number, or it may be as Langley ('92 a) has intimated, to the fact that these large afferent fibers are not fibers of general sensibility.
 
 
STRUCTURE OF THE THORACIC PORTION OF THE TRUXCUS
 
 
SYMPATHICUS
 
 
In order to understand the structure of the sympathetic trunk it is necessary to think of it as a ganglionated nerve which receives preganglionic myelinated fibers from the various white rami and through which these fibers are distributed to ganglia more or less remote from the point where the fibers enter the trunk (fig. 4).^ Above the sixth thoracic ganglion the trunks consist chiefly of ascending preganglionic fibers from the upper white rami destined to end in the upper thoracic, stellate, and cervical ganglia. Below the tenth thoracic ganglion it consists chiefly of descending preganglionic fibers from the lower thoracic and lumbar white rami to the more caudal ganglia of the trunk and to the splanchnic nerves. From the sixth to the ninth ganglia it contains both ascending and descending preganglionic fibers. The lowest known origin of ascending fibers to the superior cervical ganglion is from the seventh thoracic white rami and consists of pilomotor fibers for the face and neck. Fibers ascend to the stellate ganglion from white rami as low as the ninth. The highest fibers running to the splanchnic nerve come from the fifth or possibly the fourth. Fibers from a given white ramus may be distributed to from five to ten successive ganglia of the sj-mpathetic trunk, though the branches of an individual preganglionic nerve fiber would be distributed to a smaller number. These statements are based on Langley's ('92 a, '00, '03 a) work on the cat. In more general terms this distribution of the fibers of the white rami has been known for many years and was well stated by Gaskell ('86). According to him, the white rami from the second to the fifth thoracic nerves, 'inclusive, in the dog are directed upward, below the fifth they are directed mainly
 
 
 
 
To the ^ heart.
 
 
 
 
 
^■^r^!^^
 
 
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Fig. 4 Diagram illustrating the course of the fibers from the thoracic white rami through the sj'inpathetic trunk in the cat. A. The course of the afferent fibers. B. The course of some of the more important groups of preganglionic fibers, those terminating in the thoracic ganglia below the stellate are not indicated
 
 
423
 
 
 
 
424
 
 
 
 
S. W. RANSON AND P. R. BILLINGSLEY
 
 
 
 
TABLE 1
 
 
 
 
Connections of the spinal nerves ivith the vertebral ganglia, so far as these supply the skin, except that of the head and the anogenital region in the cat with an anterior arrangement of the spinal nerves — after Langley-Schafer's Physiology, vol. 2, p. 634
 
 
 
 
SPINAi, NERVE
 
 
 
 
IV
 
 
V
 
 
VI
 
 
VII
 
 
VIII
 
 
IX
 
 
X
 
 
XI
 
 
XII
 
 
XIII
 
 
I
 
 
II
 
 
III
 
 
 
 
SYMPATHETIC GANGLIA
 
 
 
 
G St
 
 
G St
 
 
G St
 
 
G St 4, 5, 6, 7, 8, 9
 
 
G St 4, 5, 6, 7, 8, 9, 10
 
 
(G St) 4, 5, 6, 7, 8, 9, 10, 11
 
 
8, 9, 10, 11, 12, 13
 
 
12, 13, 1, 2, 3
 
 
13, 1, 2, 3, 4 (5) (6)(7)
 
 
1, 2, 3, 4 (5) (6) 7 (1)
 
 
2, 3, 4 (5) (6) 7, 1, 2
 
 
3, 4 (5) (6) 7, 1, 2, 3
 
 
4 (5) (6) 7, 1, 2, 3 Coc.
 
 
 
 
SPINAL NERVE
 
 
 
 
IV
 
 
V
 
 
VI
 
 
VII
 
 
VIII
 
 
IX
 
 
X
 
 
XI
 
 
XII
 
 
IXII
 
 
I
 
 
II
 
 
III
 
 
 
 
downward. This is associated with the course of the fibers of which they are composed which pass not only into their segmental ganglia, but also upward into the cervical ganglia, downward into the lumbar and sacral ganglia and outwards into the collateral ganglia. Miiller ('09) has shown that the preganglionic fibers in man have a similar distribution. The connections of the spinal nerves with the ganglia of the sympathetic trunk so far as these supply vasomotor, pilomotor, and secretory fibers to the skin has been worked out in detail by physiological methods and is expressed in table 1. This shows that these preganglionic fibers from the nerves above the seventh thoracic are directed upward from the nerves below the tenth downward and from the seventh to the tenth, inclusive, both up and down.
 
 
With the exception of the cervical and stellate ganglia, which contain other elements also, the ganglia of the sympathetic trunk may be regarded as aggregations of postganglionic pilomotor, vasomotor, and secretory neurones whose axons are distributed through the corresponding gray rami and spinal nerves. As we have stated before, the fibers of a gray ramus arise from the associated sympathetic ganglion, though a few fibers may
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 425
 
 
come from the next higher or next lower ganghon. The gangha and gray rami are therefore more nearly segmental than the white rami. As we shall see, few if any postganglionic fibers, arising in the ganglia of the sympathetic trunk, pass by way of the splanchnic nerves to the abdominal viscera.
 
 
With these facts in mind we are prepared to understand the observations which follow and which show that the sympathetic trunk is a well myelinated nerve.
 
 
The sympathetic trunk caudad to the sixth thoracic ganglion has the structure shown in figure 5. It consists like other portions of the thoracic trunk of two fascicles which, though not sharply separated from each other by connective-tissue septa, maintain their identity throughout, and in cross-sections of the stained nerve are easily distinguished from each other because of their markedly different fiber content. The larger fascicle, well myelinated, presents in cross-section a round outline and occupies the greater part of the area of the cross-section. The other, which makes up but a small part of the area, is composed almost exclusively of unmyelinated fibers, and is flattened out like a crescent upon the surface of the larger bundle. For convenience of reference and until its nature is better known we will speak of this bundle as the crescent. The larger, more rounded, area will be referred to as the oval.
 
 
When followed in serial sections the crescent of unmyelinated fibers is seen to enter the ganglion at either end of the internodal segment and become lost in the ganglion. The crescent contains a very few fine myelinated fibers, and has in fact the structure of a gray ramus. The fibers of the larger well myelinated bundle, the oval, run in part into the ganglion at either end of the internodal segment, but in even larger part pa^s by along the side of the ganglion. "Every internodal segment of the thoracic sympathetic trunk presents this separation into two fascicles — and in every case where serial sections of an internodal segment, including the ganglia at both ends, were examined the crescent was found to be continuous from ganglion to ganglion.
 
 
The same structure was described as a peripheral fascicle of unmyelinated fibers in the cervical sympathetic trunk. As
 
 
 
 
426
 
 
 
 
S. W. RANSON AND P. R. BILLINGSLEY
 
 
 
 
the fascicle was followed caudad from the superior cervical ganglion it was seen to give off very small bundles of fibers w^hich left the trunk as gray branches, bringing about a gradual reduction in the size of the fascicle. One set of serial sections of the entire cervical portion of the sympathetic trunk was prepared,
 
 
 
 
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Pig. 5 The sixth thoracic internodal segment of the sympathetic trunk in the cat. Two fascicles may be recognized, one appearing in the cross-section as a large oval well myelinated field, the other as a crescentic field with few mj-elinated fibers. Osmic acid. X 425.
 
 
and in this preparation it was found that in tracing the crescent downward it decreased in size and finally disappeared. It is obvious, therefore, that in the upper cervical region a fascicle similar to the crescent consists of postganglionic fibers which accompany the trunk for a certain distance before being given off
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 427
 
 
in grsiy branches. In the thoracic region one cannot often see this fascicle of the trunk give off branches. It appears rather to serve as a commissural cord joining two successive ganglia together.
 
 
There are three possibilities concerning the nature of the fibers of this fascicle: 1. It may consist of commissural fibers arising from the cells of one ganglion and running to another. Against this assumption is all the evidence presented by Langley to show that such commissural neurones do not exist. The most important evidence in this connection is that based on degeneration experiments. Langley has shown ('03 b) that after degeneration of the lower thoracic and lumbar spinal roots, the lower part of the sympathetic trunk is in the same condition as after injection of nicotine. Stimulation between the ganglia has either no effect or only such effect as could be interpreted as due to postganglionic fibers. The literature on this question was considered at some length in the second paper of this series on page 320. In the paper by Dr. Johnson this question is again considered, and what seems to be conclusive evidence is presented that no commissural fibers exist in the sympathetic trunk of the frog. In view of these facts, it does not seem probable that the crescent is composed of commissural fibers.
 
 
2. The crescent may consist of fibers belonging to gra}' rami which ascend or descend in the trunk for a short distance. From what has been said about the crescent in the cervical region and from the fact that, as we have already stated, the fibers of a given gray ramus may come in part from the ganglion next above or next below, it seems obvious that some at least of the fibers of the crescent must be of this nature. Since, however, gray ramus fibers do not ascend or descend in the trunk for more than one segment and since such fibers are not numerous nor constantly present, it seems doubtful if they can account for the large number of fibers constantly present in the crescent.
 
 
3. A third possibility is that the crescent is formed by unmyelinated terminal branches of preganglionic fibers. There is some evidence that these fibers ma}^ lose their sheaths before terminating. This evidence has been summarized by Langley ('00) as follows :
 
 
 
 
428 S. W. RANSON AND P. R. BILLINGSLEY
 
 
By the degeneration and by the nicotine method, it can be shown that in the cat fibers run from the upper himbar white rami to the sacral and coccygeal ganglia without passing through nerve cells. In the rabbit the nicotine method only has been tried; it gives the same results. We may then conclude that in the rabbit there are preganglionic fibers, stretching from the upper lumbar white rami to the sacral coccygeal ganglia. But since the sympathetic in the sacral and coccygeal region of the rabbit contains very few medullated fibers, it follows that the preganglionic fibers in this region must be non-medullated, and as they are medullated in the white rami they must become non-medullated in passing down the sympathetic chain. In other words, preganglionic fibers may become non-medullated some distance from their termination in the vertebral ganglia.
 
 
But after all has been said it must be admitted that we are not in possession of a satisfactory explanation of the bundle of unmyelinated fibers which we have provisionally called the crescent and we do not know what the source of its fibers may be.
 
 
As seen in figure 5, the myelinated fibers which constitute the larger oval field are of various sizes. The small fibers 1.5 to S.S/x in diameter are by far the most numerous. They have the size and appearance of white rami fibers with somewhat thicker sheaths than is usual on postganglionic fibers of the same caliber. The larger fibers are rather conspicuous but are not present in great numbers. They will be recognized as the large fibers of the white rami which, as we have seen, take their origin from the dorsal root ganglia.
 
 
Sections stained with osmic acid through successive internodal segments from the sixth thoracic downward to the origin of the first splanchnic nerve show no great change in structure. There is obvious a rather considerable increase in area of the oval myelinated fascicle without any regular increase in the area of the crescent. The most noticeable feature is, however, the absolute and relative increase in the number of large myelinated fibers. A comparison of figures 5 and 6 will show that they are relatively much more numerous in the eleventh thoracic internodal segment than in the sixth. And the area of the cross-section at the eleventh is much greater than at the sixth. This increase in area is caused by the large number of fibers descending in the trunk to enter the splanchnic nerves. All of the large fibers of
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 429
 
 
the lower eight thoracic white rami turn downward toward the splanchnic nerves, and accumulate in the trunk. It is probable that many of them branch on their way down. Langley ('00) states that the large fibers of the sympathetic system occasionally divide. In this case the branches are of somewhat less diameter than the parent fibers. He does not state how these observations were made, but most of his histological observations were made on teased preparations. As evidence that division of the large
 
 
 
 
 
 
 
 
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poor\°°j°'?;
 
 
 
 
 
 
 
ojl>o^9-^o
 
 
 
 
o,
 
 
 
 
Fig. 6 A small part of a section of the eleventh thoracic internodal segment in the cat. Osmic acid. X 425.
 
 
fibers occurs in the sympathetic trunk we may mention the results of the enumeration of the large fibers in the lower thoracic white rami and in the trunk just above the origin of the first splanchnic nerve. Only fibers 6^ or greater were counted. The total number of large fibers in the lower eight thoracic white rami was 864. In the trunk just above the origin of the first splanchnic nerve there were 464, i.e., a little more than half as many as in the rami. Since, as we shall see, all or practically all of the large fibers from these rami turn downward in the trunk, and since none or almost none are given off in any of the other
 
 
 
 
430 S. W. RANSON AND P. R. BILLINGSLEY
 
 
branches of the truncus, and since being sensory fibers, it is not Ukely that they terminate in the ganglia, the simplest explanation of these numerical results would be that through branching about half of them became reduced in size below a -diameter of 6m.
 
 
In serial sections of the sympathetic trunk with the white rami attached it is easy to trace the course of the myelinated fibers from the latter. In one cat longitudinal serial sections of the trunk at the level of the entrance of the sixth white ramus were prepared from osmic acid material, also similar sections of the trunk at the level of the seventh white ramus. These rami joined the trunk at the level of the lower end of the corresponding ganglia and could be seen to divide into two bundles, a smaller ascending and a larger descending bundle. The majority of the fibers do not plunge directly into the ganglion, but seem to run by on its surface. This is especially evident in case of the descending bundle which can be followed into the trunk below the ganglion. It is very easy to follow the large medullated fibers and to see that practically all of these in the sixth and seventh white rami turn downward past the ganglion into the internodal segment.
 
 
An instructive set of preparations was obtained from another cat in which the seventh thoracic ganglion and the associated rami were cut into transverse serial sections. The white ramus on reaching the ganglion divided into two parts : the smaller of the two joined the mj-elinated portion of the truncus on the surface of the ganglion; the other part turned downward in a welldefined fascicle separated from the ganglion by a connectivetissue septum and could be traced downard for a considerable distance along the side of the seventh thoracic internodal segment before it joined with the trunk. So far as could be determined all the large fibers of this white ramus turned downward in this fascicle. Such a separate-descending fascicle is of course at^^pical, but this ramus serves to indicate in a diagrammatic way the course taken by the fibers of the white rami on entering the trunk. Of course the corresponding fibers of the upper thoracic white rami turn upward instead of downward.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 431
 
 
At the point where the first and largest splanchnic nerve is given off, which is usually near the thirteenth thoracic ganglion, the size of the trunk becomes abruptly reduced, and it is obvious, when serial sections are studied, that a large part of its myelinated fibers run into this nerve.
 
 
The sympathetic trunk cephalad to the sixth thoracic ganglion is characterized by the small number of large myelinated fibers which it contains. The peripheral crescent-like bundle of unmyelinated fibers is seen here as well as in lower segments and can be traced continuously from one ganglion into another. Above the fourth thoracic ganglion the trunk sometimes breaks up into two or three fascicles w^hich run parallel to one another to
 
 
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Fig. 7 One of three fascicles composing the sympathetic trunk al)ove tiie level of the fourth thoracic ganglion in the cat. Osmic acid. X 425.
 
 
reach the stellate ganglion. A cross-section of such a fascicle just above the level of the fourth thoracic ganglion is seen in figure 7. The crescent of unmyelinated fibers was joined with one of the other two fascicles of which the trunk was composed. The fascicle which is seen in cross-section in figure 7 contained no bundle of unmyelinated fibers large enough to be recognized in osmic acid preparations. With the exception of two larger fibers, it was composed of myelinated fibers of uniformly small size. The other fascicles of the trunk were also characterized by the paucity of large and medium-sized myelinated fibers.
 
 
 
 
432 S. W. RANSON AND P. R. BILLINGSLEY
 
 
In studying the white rami we have found reason for beheving that the large and medium-sized fibers of the sympathetic system are afferent. There are also small myelinated afferent fibers, but these are not readily distinguished from the preganglionic efferent fibers. It will be evident from what has been said that the large and medium-sized myelinated afferent fibers are present in varying numbers in different parts of the thoracic sympathetic trunk. Between the stellate ganglion and the sixth thoracic ganglion they are few in number. Caudal to the sixth ganglion there is a steady increase in these fibers with the accession of each successive white ramus until the point of origin of the greater splanchnic nerve is reached through which nerve a large part of these fibers run toward the viscera (fig. 4 B). We shall now see that unmyelinated afferent fibers from the white rami are distributed in the same way as these myelinated sensory fibers which we have been studying.
 
 
Above the level of the fourth thoracic ganglion there are very few unmyelinated fibers in the trunk except for the well-defined bundle which we have referred to as the crescent. The fine myelinated fibers of which the rest of the cross-section is composed are almost free from an admixture of unmyelinated fibers. These are also not very numerous in the oval of the seventh internodal segment. In the lower thoracic segments the oval well myelinated portion of the section does not consist entirely of myelinated fibers, but, as is shown in figure 8, it contains also very large numbers of unmyelinated axons. These are grouped in small bundles which lie among the myelinated fibers. The distribution of the three kinds of fibers, large myelinated, small myelinated, and unmyelinated, is not uniform throughout the cross-section. The large myelinated fibers are much more numerous in some parts of the field than in others (fig. 5) . They also show a tendency to be arranged in bundles which are separated from each other by the small myelinated fibers. Now it is in and about these bundles of large myelinated fibers that the greatest number of the unmyelinated axons are found. The grouping of these with the large myelinated sensory fibers suggests that they also may be afferent in function. The data thus
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 433
 
 
far presented would not exclude the possibility that these Linmyelinated fibers might be preganglionic fibers that had lost their myelin sheaths, but in the paper which follow^s we will present evidence to show that they are afferent fibers and arise from the cells in the spinal ganglia.
 
 
Since there are few large myelinated and unmyelinated fibers
 
 
 
 
 
 
 
Fig. 8 A part of a section through the tenth thoracic internodal segment in the cat. Pj'ridine silver. X 425.
 
 
in the sympathetic trunk below the stellate ganglion and practically none in the cervical part of the trunk, we must conclude that the sensory fibers which reach the stellate ganglion by way of the first three white rami run out again through the branches of the stellate or the inferior cervical ganglion. These branches have been studied in only one cat. The cardiac branch of the stellate ganglion, while consisting chiefly of unmyelinated fibers, contained a somewhat larger number of myelinated fibers than
 
 
THE JOURNAL OF COMP.\.RATIVE NEUROLOGT, VOL. 29, NO. 4
 
 
 
 
434 S. W. RANSON AND P. R. BILLINGSLEY
 
 
the internal carotid nerve. These were all under 4.5^ except two, which measured 6^. Large myelinated fibers were found in both limbs of the subclavian ansa which joined to farm a single trunk just below the middle cervical ganglion. A cardiac branch given off by the trunk in this position contained a considerable number of fibers between 4.5 and 7^. We counted forty-eight that measured approximately 6^. Aside from the presence of these larger fibers, this nerve had the same structure as the cardiac branch of the stellate ganglion. These observations indicate that the large myelinated fibers pass through the stellate ganglion, run in both limbs of the ansa, and leave through the cardiac branch coming from the middle cervical ganglion or from the ansa subclavia. This is in keeping with the work of Edgeworth ('92), who found that the large myelinated fibers in the dog could be followed in the stellate ganglion through the ansa subclavia and middle cervical ganglion, whence they were distributed to the heart and lungs. This question deserves thorough study. As is indicated in figure 4 B, the sensory fibers from the lower eight thoracic rami run downward in the trunk and out through the splanchnic nerve. In the segments just below the stellate ganglion there are few large myelinated and unmyelinated sensory fibers, as is indicated in the diagram by the dotted line.
 
 
THE GREATER SPLANCHNIC NERVE
 
 
At another time we expect to take up the more detailed consideration of all the splanchnic nerves of the cat, but the present paper would not be complete without some account of the structure of the first and largest of the series, the greater splanchnic nerve. A study of serial sections through the trunk at the point of origin of this nerve shows clearly that it is formed by the separation of a large part of the oval well myelinated fascicle from the rest of the trunk. The nerve has the same structure as this oval fascicle and consists of large and small myelinated and unmyelinated fibers in the same proportion and with the same arrangement as in that fascicle.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 435
 
 
Usually in pyridine silver preparations it is possible to see that there are somewhat larger accumulations of unmyelinated fibers near the periphery or dil^ectly under the perineurium. These do not constitute well-defined fascicles such as one would expect to find if any large number of postganglionic fibers were present. They are probably of the same nature as those scattered through the nerve.
 
 
In two out of ten normal greater splanchnic nerves examined we found evidence of postganglionic fibers in the form of a welldefined and fairly good-sized fascicle composed chiefly of unmyelinated fibers. Preparations of the first lumbar segment of the sympathetic trunk and the greater splanchnic nerve taken
 
 
Jf.splanch.mal. \M3pla.ncn.rnm.
 
 
Fig. 9 Diagram of the upper lumbar portion of the sympathetic trunk of a cat in which there was an accessory ganglion at the origin of the greater splanchnic nerve. XIII. VV., white ramus to the XIII thoracic nerve; I. G., gray ramus to the I lumbar nerve; I. W., white ramus of the I lumbar nerve; II. G., gray ramus to the II lumbar nerve.
 
 
from Cat 8 were especially instructive. Figure 9 shows that in the first lumbar segment of the trunk there was a ganglion, not connected with the spinal nerves by rami, located at the point of origin of the greater splanchnic nerve. The entire portion of the sympathetic trunk shown in the figure was cut in serial sections. A study of these sections shows that no branches, even of microscopic size, are given off from the trunk at the level of this ganglion except the splanchnic nerve. As this nerve leaves the trunk it carries with it a rather large bundle of peripherally placed unmyelinated fibers which closely resembles the crescentic area described in the trunk. It seems probable that this unusual bundle of fibers takes origin from the cells in this aberrant ganglion.
 
 
The observations so far recorded lead one to conclude that the greater splanchnic nerve is composed chiefly of preganglionic
 
 
 
 
436 S. W, RANSON AND P. R. BILLINGSLEY
 
 
autonomic fibers and visceral afferent fibers. In the majority of the specimens studied (eight out of ten) it was not possible to demonstrate any group of fibers that could be identified as postganglionic. We shall see that these conclusions agree with those of Langley. The statements which appear in the citation below will be found scattered through several pages of text (Schafer's Physiology, vol. 2, pp. 644, 646, 648) :
 
 
By dissection, it is easy to see that a large proportion of the splanchnic nerve fibers arise from the white rami commimicantes, running in the sympathetic chain for a variable distance. In the cat and dog the fibers of the great splanchnic nerve can be traced upwards in the sympathetic chain as far as the sixth thoracic ganglion. And there is good reason to believe that all the splanchnic fibers are the direct continuation of the fibers of the white rami. It can easily be shown in the rabbit that the verj^ great majorit}^ of the" fibers running from the spinal cord to the abdominal viscera end in the prevertebral ganglia. After injection of a small amount of nicotine in the rabbit, the nerve roots, the splanchnics proper, and the inferior splanchnics have either no effect or a mere trace on the blood vessels or abdominal and pelvic viscera; but all the normal effects can be readily obtained by stimulating the fibers given off by the preverteh-al ganglion. It has long been known that the major splanchnic contains a considerable number of non-medullated fibers, and it is in large part this fact which has led to the unquestioned belief that the ganglia of the sympathetic chain send fibers to the solar ganglia or to the abdominal viscera. If, then, the view which I have given above be accepted, namely, that very few if an}^ fibers pass from the cells of the vertebral ganglia to the splanchnic nerves, we must take the nonmedullated fibers to be preganglionic fibers which have lost their medulla.
 
 
According to Langley, the majority of the efferent fibers of the greater splanchnic terminate in the solar ganglion, though a few may pass on to more distal ganglia. He also admits the possibility that occasionally a few postganglionic fibers arising from cells in the ganglia of the trunk may run through the splanchnic to the coeliac plexus. The ph3^siological experiments on which his conclusions are based are found in the papers by Langley and Dickinson ('89), Langley ('96 b), and Bunch ('97).
 
 
It will be seen that our histological results are in agreement with those obtained by physiological experimentation. We have seen reason to believe that the unmyelinated fibers in the splanchnic which Langley thought might be preganglionic fibers that had lost their sheaths, are instead afferent fibers. More convincing
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 437
 
 
evidence on some of these points will be presented in the paper which follows.
 
 
CONCLUSIONS
 
 
We shall make no attempt to summarize the detailed observations presented in the preceding pages, but will merely state a few general conclusions that seem warranted by the facts already given.
 
 
The segmental character of the sympathetic trunk is evident in its ganglia and gray rami. The fibers of each gray ramus arise chiefly, and sometimes exclusively, from the cells of its own segmental ganglion and are distributed through its associated spinal nerve. When two or more segmental ganglia are fused together the resulting compound ganglion gives rise to gray rami running to the corresponding spinal nerves. Except for compound ganglia like the cervical and stellate, the ganglia of the trunk are best designated by the number of the spinal nerve with which their gray rami are associated. The white rami have a restricted origin from the first thoracic to the fourth lumbar spinal nerves, inclusive, and their fibers are distributed through the sympathetic trunk to ganglia at higher and lower levels. A white ramus is in no special sense associated with its own segmental ganglion.
 
 
The gray rami contain in addition to the unmyelinated also a few, mostly fine, myelinated fibers. The latter are for the most part postganglionic. No preganglionic fibers run from the spinal cord to the sympathetic ganglia by way of these rami.
 
 
The white rami consist of myelinated fibers ranging from 1.5 to 13m, though fibers of more than lO/x are rare except in the first two white rami and most of the large fibers have a diameter of about 6 or T^i. The majority of the myelinated fibers are small, measuring 1.5 to 3.5^. Most of these are preganglionic. The afferent components include myelinated fibers of all sizes, some of the very smallest as well as those of medium and large size, and also unmyelinated axons. The number of the large myelinated fibers varies greatly in the different white rami. They were found to be most numerous in the seventh to the tenth,
 
 
 
 
438 S. W. RANSON AND P. R. BILLINGSLEY
 
 
from which they run through the sympathetic trunk and the splanchnic nerves to the viscera.
 
 
The sympathetic trunk is to be looked upon as a series of more or less segmentally arranged ganglia bound together by fibers frcm the white rami. Above the sixth thoracic ganglion these fibers are chiefly ascending, below the tenth descending, but between the sixth and tenth both ascending and descending fibers are present. In addition to these fibers from the white rami, which make up the larger part of the cross-section of the trunk in the form of a large well myelinated oval field, there is also present throughout the thoracic sympathetic trunk a small well-defined bundle consisting chiefly of unmyelinated fibers. This in cross-sections appears flattened out like a crescent against the larger oval well myelinated field. Some of the fibers in the crescentic field are postganglionic, ascending or descending to reach adjacent gray rami. Others may be preganglionic fibers that have passed through one or more ganglia, giving off collaterals tnd losing their myelin sheaths.
 
 
In the upper part of the thoracic sympathetic trunk the oval well myelinated field is composed almost exclusively of fine myelinated preganglionic fibers, with very few large myelinated and unmyelinated afferent fibers. In the lower thoracic segments there are in addition to the preganglionic components also afferent fibers, both myelinated and unmyelinated, which increase steadily in number from the sixth intern odal segment toward the origin of the greater splanchnic nerve.
 
 
The greater splanchnic nerve of the cat usually leaves the trunk at or just below the level of the thirteenth thoracic ganghon. It is formed by the separation of a large part of the oval well myelinated fascicle from the rest of the sympathetic trunk and is composed of fine myelinated preganglionic fibers, destined to end in the coeliac ganglion, and of both myelinated and unmyelinated afferent fibers. Occasionally it also contains a bundle of postganglionic fibers arising from cells in ganglia of the sympathetic trunk.
 
 
 
 
THORACIC TRUNCUS SYMPATHICUS 439
 
 
LITERATURE CITED
 
 
Bidder and Volkman 1842 Die Selbstandigkeit des sympathischen Nerven systems. Leipzig, 1842. Bunch, J. L. 1898 On the origin, course and cell-connections of the visceromotor nerves of the small intestine. Jour. Physiol., vol. 22, p. 357. Edgeworth, F. H. 1892 On a large-fibered sensory supply of the thoracic and
 
 
abdominal viscera. Jour, of Physiol., vol. 13, p. 261. Gaskell, W. H. 1886 On the structure, distribution and function of the nerves
 
 
which innervate the visceral and vascular systems. Jour. Physiol.,
 
 
vol. 7, p. 1. Langley, J. N., AND Dickinson, W. L. 1889 On the local paralysis of peripheral
 
 
ganglia, and on the connection of different classes of nerve fibers with
 
 
them. Proc. Roy. Soc. London, vol. 46, p. 423. Langley, J. N. 1891 a On the course and connections of the secretory fibers
 
 
supplying the sweat glands of the feet of the cat. Jour, of Physiol.,
 
 
vol. 12, p. 347.
 
 
1891 b Note on the connection with nerve-cells of the vasomotor nerves for the feet. Jour, of Physiol., vol. 12, p. 375.
 
 
1892 a The origin from the spinal cord of the cervical and upper thoracic sympathetic fibers, with some observations on white and gray rami communicantes. Phil. Trans. Roy. Soc. London, vol. 183, p. 114. 1892 b On the larger meduUated fibers of the sympathetic system. Jour, of Physiol., vol. 13, p. 786.
 
 
1894 The arrangement of the sympathetic nervous system, based chiefly on observations upon pilo-motor nerves. Jour, of Physiol., vol. 15, p. 176.
 
 
1896 a Observations on the medullated fibers of the sympathetic system and chiefly on those of the gray rami communicantes. Jour, of Physiol., vol. 20, p. 55.
 
 
1896 b On the nerve cell connection of the splanchnic nerve fibers. Jour, of Physiol., vol. 20, p. 223.
 
 
1900 The sympathetic and other related systems of nerves. Schjifer's Physiology, vol. 2, p. 616.
 
 
1903 a The autonomic nervous system. Brain, vol. 26, p. 1. 1903 b Das sympathische und verwandte nervose Systeme der Wirbeltiere. Ergebn. d. Physiol., vol. 2, p. 818. MtJLLER, R. L. 1909 Studien iiber die Anatomie und Histologic des sympathischen Grenzstranges, insbesondere liber seine Beziehungen zu den spinalen Nervensysteme. 26. Kongr. innere Med., Wiesbaden, p. 658. Ref. in Jahres. Anat. u. Entwick., vol. 15, III, p. 731.
 
 
 
 
adthor's abstract op this paper issued bt the bibliographic service, mat 11
 
 
 
 
AN EXPERIMENTAL ANALYSIS OF THE SYMPATHETIC
 
 
TRUNK AND GREATER SPLANCHNIC NERVE
 
 
IN THE CAT
 
 
S. W. RANSON AND P. R. BILLINGSLEY
 
 
Anatomical Laboratory of the Northwestern University Medical School^
 
 
TEN FIGURES
 
 
A consideration of the facts presented in the preceding paper makes it clear that much could be learned through the study of the sympathetic trunk and splanchnic nerves after a variety of experimental lesions leading to the degeneration of nerve fibers arising from the spinal cord and spinal ganglia. We have five experiments to record, and since no two were just alike it will be best to consider each separately. The operations were performed under rigid asepsis. The general technique of exposing the spinal cord and nerve roots has been given in another place (Ranson and v. Hess, '15). After time had been allowed for degeneration, the lesion was verified at autopsy and the affected portion of the sympathetic trunk with its rami communicantes and the greater splanchnic nerve was removed and prepared for microscopic examination by fixation in osmic acid or by the pyridine silver technique. So far as was possible the material was cut into serial sections. The details of the five experiments follow.
 
 
Cat XL Died seven days after the left sympathetic trunk was cut below the ninth thoracic ganglion and the ninth thoracic to the first lumbar spinal nerve roots cut proximal to the spinal ganglia as shown in figure 1. Examination of the gray rami of the tenth, eleventh, and twelfth thoracic nerves, showed that the few fine myelinated fibers which they normally contain were not in the process of degeneration. That is to say, these are not
 
 
1 Contribution No. 59, February 15, 1918.
 
 
441
 
 
 
 
442
 
 
 
 
S. W. RANSON AND P. R, BILLINGSLEY
 
 
 
 
preganglionic efferent fibers coming from the spinal cord (page 421). The white rami of these three nerves showed marked changes. Most of the small myelinated fibers were undergoing degeneration, but there were a few which in cross-section appeared as sharply contoured black rings. These were apparently normal as were also all of the large myelinated fibers. In the trunk
 
 
 
 
 
 
 
 
 
Fig. 1 Diagram of the thoracic sympathetic trunk with the corresponding spinal nerves and rami communicantes to illustrate lesions produced in cats IX and XII. The course of the degenerated fibers is indicated in black. N.S.M. = N. splanchnicus major.
 
 
Fig. 2 Diagram of the thoracic sympathetic trunk with the corresponding spinal nerves and rami communicantes to illustrate the lesions produced in cat VII. The course of the degenerated fibers is indicated in black. N.S.M. = N. splanchnicus major.
 
 
 
 
above the level of the tenth ganglion, i.e., between the lesion and the next lower ganglion, the oval field described in the preceding paper (fig. 5, page 426), was largely degenerated. Nearly all of the fine myelinated fibers were represented by
 
 
 
 
ANALYSIS OF THE SYMPATHETIC TRUNK 443
 
 
myelin globules, though a very few of them retained a normal appearance. There was very little degeneration of the large fibers, and, since the fibers present at this point must nearly all have been cut away from their cells of origin, we must interpret this result as showing that sufficient time had not elapsed for the degeneration of the large fibers. It has been shown by Van Gehuchten and Molhant ('10) that the speed of degeneration in myelinated fibers is inversely proportional to their size. In parts of the crescentic field the scattered fine myelinated fibers were normal, in other parts of this same field they were all degenerated.
 
 
A cross-section of the trunk below the tenth ganglion showed most of the scattered fine myelinated fibers in the crescentic field to be normal in appearance, indicating that few of them took origin above the cut. The oval field had the same appearance as in the section described above. The tenth white ramus could be seen in longitudinal section as it entered the trunk. The majority of its fine myelinated fibers had their myelin broken up into globules, giving them a beaded appearance. Its large fibers and a few of the small ones were normal.
 
 
Sections of the greater and lesser splanchnic nerves showed that most of the fine myelinated fibers were degenerated, while the large fibers were all or nearly all normal. These results were confirmed by a study of teased preparations of the twelfth internodal segment of the trunk and the greater splanchnic nerve. In these teased preparations it was possible to see that a few large fibers were also in the early stages of degeneration.
 
 
Cat VII, killed thirty-three days after section of the roots of the left tenth, eleventh, twelfth, and thirteenth thoracic and first lumbar nerves proximal to the spinal ganglia as indicated in figure 2.
 
 
Sections of the trunk below the entrance of the tenth white ramus showed a circumscribed area of degeneration at the surface of the trunk. In this area there were two large and a considerable number of small normal myelinated fibers. This degenerated area was taken to represent the tenth white ramus, although enough sections were lost from the series at this level to prevent our tracing that ramus directly into the degenerated area.
 
 
 
 
444 S. W. RANSON AND P. R. BILLINGSLEY
 
 
The white ramus of the eleventh thoracic nerve contained myeUnated fibers of all sizes in about equal proportions. These were scattered fairly evenly throughout the cross-section and were separated by a large amount of degenerative material (fig. 3). It was obvious that the preganglionic fibers had degenerated as the result of the section of the ventral root. The fibers which remained were afferent and arose from the cells in the spinal ganglia. These afferent myelinated fibers were of all
 
 
 
 
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Fig. 3 Eleventh thoracic white ramus of the cat after the degeneration of all the preganglionic efferent fibers. All of the remaining fibers are afferent. Osmic acid. X 425.
 
 
 
 
sizes, as is shown in the illustration, but as a rule there are relatively more large ones than in this ramus.
 
 
In the serial sections the degenerated eleventh white ramus could be traced into the trunk above the level of the twelfth thoracic ganglion (fig. 4 a). Here it occupied a position superficial to that occupied by the degenerated fibers from the tenth (fig. 4 b). The rest of the oval field was occupied by large and small myelinated fibers and was normal in appearance. Only a small part of this is shown in the illustration.
 
 
 
 
ANALYSIS OF THE SYMPATHETIC TRUNK 445
 
 
A little farther down in the trunk the fibers derived from the tenth and eleventh white rami formed a single well-defined bundle which because of the degeneration was easily distinguished from the normal part of the trunk. This degenerated bundle could be traced through the trunk beyond the origin of the first splanchnic nerve. None of the degenerated fibers seemed to go
 
 
 
 
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Fig. 4 From the eleventh thoracic internodal segment of the sympathetic trunk of cat VII, showing the partially degenerated fascicles derived from a) the eleventh and b) the tenth white ramus. Osmic acid. X 260.
 
 
into the greater splanchnic nerve, which was normal in appearance and seemed to receive all or nearl}^ all of the undegenerated oval well myelinated portion of the trunk. In this case all of the fibers of the greater splanchnic nerve came from the white rami above the tenth. In one instance it received a few fibers from the tenth white ramus (Cat XIV) in another (Cat XVI) all of its fibers came from above the ninth.
 
 
 
 
446 S. W. RANSON AND P. R. BILLINGSLEY
 
 
Above the level of the eleventh ganglion there was some evidence of degeneration, and this could be followed up as far as the tenth. The evidence of an ascending degeneration was, however, by no means as clear as that for a descending degeneration.
 
 
The gray rami of the eleventh, twelfth, and thirteenth thoracic nerves were normal, containing a few fine myelinated fibers. No axon stain was made. The white ramus of the tenth nerve was not well stained, that of the eleventh nerve has already been described and figured. The twelfth white ramus contained a fair number of medium and small-sized fibers, but no large ones. Most of the normal fibers in the thirteenth white ramus were also of medium and small size. It is clear that in these rami of this cat the afferent fibers were for the most part of medium and small size. We regard the paucity of large fibers as somewhat atypical.
 
 
The point which stands out most clearly as a result of this experiment is that the majority of the fibers of the tenth and eleventh white rami turn downward in the trunk, forming a welldefined fascicle near its surface which can be traced in the trunk beyond the origin of the great splanchnic nerve. At least in the upper part of this course the fibers from the two rami remain separate, those from the eleventh lying superficial to those of the tenth. This lamination of the fibers in the trunk in flattened bundles, corresponding to the white rami from which they come, explains why it is easy to follow these fibers by dissection through the trunk to the splanchnic nerve, as is claimed by Langley
 
 
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The degeneration of the preganglionic fibers in the lower thoracic white rami enables us to isolate the myelinated sensory fibers and to see that these include fibers of all sizes. These can be seen not only in the rami themselves, but also in the degenerated fascicles representing these rami in the trunk.
 
 
Cat XII. The sympathetic trunk was cut on the left side at the level of the ninth internodal segment and the roots of the left ninth, tenth, eleventh, twelfth, and thirteenth thoracic and first lumbar nerves were cut proximal to the spinal ganglia, as shown in figure 1. The cat was killed thirteen days after the operation.
 
 
 
 
ANALYSIS OF THE SYMPATHETIC TRUNK 447
 
 
The gray rami of the tenth, eleventh, twelfth, and thirteenth thoracic nerves were normal, containing the usual small number of fine myelinated fibers, except that in the tenth there were four or five fine fibers which did not appear normal. The white rami of these nerves were in large part degenerated, although scattered through each there were a considerable number of myelinated fibers of all sizes. The proportion of large and small fibers did not seem to be constant. These undegenerated fibers might, so far as the data given by this experiment is concerned, have had their cells of origin in the spinal ganglia or in the ganglia of the sympathetic trunk. Other experiments will show that the cells were located in the spinal ganglia.
 
 
The part of the trunk including the tenth thoracic ganglion and internodal segment was fixed in osmic acid and cut into serial sections. Just below the tenth ganglion all the fibers in the trunk were degenerated. Many of the larger myelinated fibers were still seen in process of degeneration. A little lower down a very small branch was seen entering the trunk, probably an accessory white ramus from the tenth nerve, which contained eleven myelinated fibers chiefly of medium size. These could be followed down in the trunk as a small compact fascicle for some distance, but became lost just above the point where the tenth white ramus entered the trunk, at which point the serial sections were imperfect, but it probably joined with the fibers from this ramus as it was not recognizable as a separate fascicle below the point where this ramus entered. Below the point of entrance of the tenth white ramus there was a well-defined fascicle of about the size of the ramus, composed of myelinated fibers of all sizes rather widely separated from each other. This fascicle from which the bulk of the fine myelinated fibers had disappeared could be followed downward at the surface of the trunk throughout the series of sections which did not include the entrance of the eleventh ramus.
 
 
The twelfth thoracic ganglion and adjacent portions of the trunk were prepared by the pyridine silver technique. Most of the fibers in the trunk were degenerated, but the crescent could be recognized and contained a great many normal fibers, the
 
 
 
 
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ANALYSIS OF THE SYMPATHETIC TRUNK 449
 
 
staining of these fibers was not very satisfactory, however. On one side of the trunk there was a rather large area containing scattered normal myelinated fibers, many of which were of large size. This area represented the contribution of the tenth and eleventh white rami, and the myelinated fibers in this area were the afferent fibers from these rami. Among these normal myelinated afferent fibers were considerable numbers of unmyelinated fibers, also of normal appearance and showing a marked tendency to arrange themselves in groups, as seen in figure 5. Throughout the rest of the trunk all the fibers, both myelinated and unmyelinated, were degenerated. The fibers in this completely degenerated area had their cells of origin located above the point of section of the trunk, and from what has already been said in this and the preceding paper we know that they entered the trunk by way of the white rami above the tenth. The tenth and eleventh white rami contributed the fibers found in the area which is only partly degenerated, and since the roots of the corresponding spinal nerves were cut proximal to the spinal ganglia the only normal fibers which these rami could contribute would be afferent with cell bodies located in the spinal ganglia. We are therefore justified in interpreting as afferent all the fibers in this area, including large and small myelinated and unmyelinated fibers.
 
 
We have both osmic acid and pyridine silver preparations of the greater splanchnic nerve. This was almost completely degenerated. There was, however, at one side a small group of normal myelinated fibers. These could be seen in both osmic acid and pyridine silver preparations. In the latter, as shown in figure 6, there were also some normal unmyelinated fibers to be seen mingled with the others. The rest of the splanchnic was completely degenerated except for a very small bundle of unmyelinated fibers on the other side of the cross-section. In connection with this bundle there were some nerve cells and the fibers of this group were probably to be regarded as postganglionic, arising from the cells of a small ganglion in the course of thd splanchnic. The bundle of myelinated and unmyelinated fibers was clearly a continuation of a part of that found in the trunk and illustrated in figure 5.
 
 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 4
 
 
 
 
450 S. W. EANSON AND P. R. BILLINGSLEY
 
 
Serial sections of the trunk including the first lumbar ganglia and the origin of the second splanchnic nerve, stained with osmic acid, were examined. In the trunk below the thirteenth thoracic ganglion and the origin of the greater splanchnic nerve the majority of the fine myeUnated fibers had degenerated. There were present, however, normal myelinated fibers of all sizes rather widely separated from each other by degenerated material. These were the afferent fibers of the tenth, eleventh, and twelfth white rami. The lesser splanchnic had the same structure as the thirteenth thoracic internodal segment.
 
 
Cat XIV. Killed thirty-two days after section of the roots of the tenth distal, and those of the eleventh thoracic nerve proximal, to the spinal ganglia (fig. 7). In osmic acid preparations of the trunk including the tenth, eleventh, and twelfth thoracic ganglia, the tenth white ramus could be seen entering the trunk. It contained six or eight normal fine myelinated fibers, but except for these was completely degenerated. It could be traced down the trunk as a sharply defined fascicle occupying a superficial position. In addition to the half-dozen fine myelinated fibers that could be traced in along with the tenth ramus this degenerated area became invaded by a few fine myelinated fibers that worked their way into it from the normal part of the trunk.
 
 
The white ramus of the eleventh nerve could also be traced into the trunk. It contained a small number of large fibers and a somewhat greater number of medium-sized and small fibers. These normal fibers were separated by a considerable amount of unstained material representing the degenerated preganglionic fibers. These normal and degenerated fibers of the eleventh white ramus could be followed down the trunk where they could be seen to occupy a position adjacent and partially superficial to the fibers from the tenth ramus.
 
 
The bundles from the two degenerated rami presented a marked contrast. That of the tenth contained only a few fine myelinated fibers, that of the eleventh a much greater number of all sizes. The latter are easily accounted for as afferent fibers with their cells of origin in the eleventh thoracic spinal ganglion.
 
 
 
 
ANALYSIS OF THE SYMPATHETIC TRUNK
 
 
 
 
451
 
 
 
 
The half-dozen fine fibers traced from the tenth ramus are more diflScult to understand. It must be admitted that such fibers are just what one would find if sensory fibers arising in the sympathetic ganglia pass back along the white rami to end in the spinal ganglia (p. 333-334). They might also be accounted for as postganglionic fibers accompanying the white^ramus (p. 412-418).
 
 
 
 
 
 
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Fig. 7 Diagram of the thoracic sympathetic trunk with the corresponding spinal nerves and rami communicantes to illustrate the lesions produced in cat XIV. N.S.M. = N. splanchnicus major.
 
 
Fig. 8 Diagram of the thoracic sympathetic trunk with the corresponding spinal nerves and rami communicantes to illustrate the lesions produced in cat XVI. N.S.M. = N. splanchnicus major.
 
 
 
 
Osmic acid preparations of the greater splanchnic nerve showed a very restricted area of degeneration, almost the entire nerve being of normal appearance.
 
 
Cat XVI. Killed twenty-two days after section of the roots of the ninth and tenth thoracic nerves proximal to the spinal ganglia (fig. 8). The trunk including the ninth, tenth, and
 
 
 
 
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eleventh thoracic gangha, stained with osniic acid, was cut into serial sections. In these it was possible to identify the ninth white ramus which contained a considerable number of normal myelinated fibers, of which the greater number were large. The fibers from this ramus could be followed as a superficial bundle down the trunk to the point where the tenth ramus entered. This contained in addition to the degenerated preganglionic fibers a considerable number of normal myelinated fibers, and of these there were rather more small than large ones. As each ramus entered it lay close to the crescentic field of unmyelinated fibers and the area of the tenth was immediately adjacent to that of the ninth, A little farther caudad it was no longer possible to separate the two areas, the two together being spread out over nearly half the circumference of the trunk as shown in figure 9. In this figure the degenerated bundles are indicated by the stippled background. The myelinated fibers in these bundles are afferent, and it will be seen that they are of all sizes and there are about as many of one size as of another.
 
 
Pyridine silver preparations of the twelfth thoracic internodal segment were especially instructive (fig. 10). The greater part of the trunk was normal and was characterized by the presence of great numbers of small myelinated fibers. Large myelinated and unmyelinated fibers were also in evidence. On one side there was seen a condensation of the unmyelinated fibers which represents the crescentic field normally present at all levels of the thoracic sympathetic trunk. Another area, rather sharply limited, from which the majority of the fine myelinated fibers had disappeared, contained myelinated fibers of all sizes in about equal proportion and also unmyelinated axons. The background presented a peculiar reddish-yellow tone which we have found characteristic of degenerated fascicles stained by this method. It is obvious that the fine myelinated fibers had degenerated and that this is the same fascicle that is seen in figure 9. A comparison of the two figures will show that the areas occupied by the degenerated fibers have undergone great shrinkage in passing through the steps of the pyridine silver technique, and because of this the large myelinated and unmyelinated fibers
 
 
 
 
454
 
 
 
 
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ANALYSIS OF THE SYMPATHETIC TRUNK 455
 
 
are more closely grouped together in figure 10, Since this partially degenerated fascicle could be traced to the white rami of the ninth and tenth thoracic nerves, the roots of which had been cut proximal to the spinal ganglia, it is clear that the normal fibers remaining in this fascicle were not preganglionic autonomic fibers. They must either have been afferent, with their cells of origin in the spinal ganglia, or they must have been directed from the sympathetic ganglia toward the spinal ganglia or spinal cord. The complete degeneration of the greater part of the trunk at the level of the twelfth thoracic internodal segment after section of the trunk below the ninth thoracic ganglion in Cat XII, as illustrated in figure 5, shows that these fibers do not take origin from the sympathetic ganglia.
 
 
The partially degenerated fascicle from the ninth and tenth white rami made no contribution to the greater splanchnic nerve, but was continued along the trunk into the lesser splanchnic. Osmic acid and silver preparations of the greater splanchnic showed that this nerve was entirely normal, while similar preparations of the lesser splanchnic showed that it had the same structure as the partially degenerated fascicle in the trunk.
 
 
SmiMARY
 
 
Section of the thoracic spinal nerve roots proximal to the spinal ganglia results in a degeneration of all of the preganglionic autonomic fibers in the corresponding white rami, but leaves the afferent fibers intact. The white rami studied were the ninth, tenth, and ele\'enth. The fibers from these partially degenerated rami could be traced caudad in the trunk, those from each ramus forming a well-defined fascicle. It is this arrangement which makes it possible to trace the fibers of the splanchnic nerve by dissection to the white rami as high as the sixth. The afferent fibers, which alone remained in these partially degenerated rami and the corresponding fascicles of the trunk, included myelinated fibers of all sizes and many that were unm^^elinated. They took origin from the cells of the spinal ganglia. In one case after section of the tenth thoracic nerve distal to the spinal ganglion we found a half-dozen normal myelinated fibers in the corre
 
 
 
456 S. W. RANSON AND P. R. BILLINGSLEY
 
 
spending white ramus, but these may have belonged to a small gray ramus accompanying it.
 
 
When the sympathetic trunk was cut caudad to the ninth thoracic ganglion all the fibers degenerated in the oval well mj'elinated field in the twelfth thoracic internodal segment, except in a fascicle derived from the tenth and eleventh white rami, which entered the trunk caudad to the cut. The fibers in this oval field, therefore, come from the spinal cord and spinal ganglia by way of the white rami ; at least this experiment proves that none of them in the twelfth thoracic internodal segment come from the ganglia of the sympathetic trunk below the ninth, and under the circumstances there is no reason to suppose that they might come from those situated farther cephalad. In this experiment the greater splanchnic nerve was degenerated except for a small bundle of fibers that could be traced into it from the fascicle representing the white rami of the tenth and eleventh nerves, and a very small number of unmyelinated fibers obviously associated with a small group of ganglion cells located in the course of the ner\'e. It is clear that in this case the splanchnic nerve received no fibers from the ganglia of the sympathetic trunk below the ninth, and there is every reason to believe that all of its fibers, except those arising from the small ganglion located in its course, came from the spinal cord and spinal ganglia (p. 434-436). Exclusive of an occasional welldefined bundle of obviously postganglionic fibers found in two out of ten normal specimens of the greater splanchnic nerve, the unmyelinated fibers of this nerve are derived from spinal ganglia by way of the white rami. The number of rami from which this nerve may receive fibers seems to vary, but it usually does not contain any from those below the ninth.
 
 
LITERATURE CITED
 
 
Laxgley, J. N. 1900 The s>aiipathetic and other related systems of nerves.
 
 
Schafer's text-book of physiology, vol. 2. Ranson, S. W., and v. Hess, C. L. 1915 The conduction within the spinal
 
 
cord of the afferent impulses producing pain and the vasomotor reflexes.
 
 
Am. Jour. Physiol., vol. 38, p. 128. Van Gehuchten, A., and Molhant, M. 1910 Les lois de la dcgenei'escence
 
 
wallerienne directe. Le Nevraxe, vol. 11, p. 75.
 
 
 
 
AUTHOR 8 ABSTRACT OF THIS PAPER IsSUED BY THE BIBLIOGRAPHIC SERVICE, JULY 19
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
N. E. McINDOO Bureau of Entomology, Washington, D. C.
 
 
FIFTY-FIVE FIGURES
 
 
CONTENTS
 
 
Introduction and methods 457
 
 
The olfactory pores 460
 
 
Disposition of pores in Musca domestica 460
 
 
a. Pores on legs 460
 
 
6. Pores on wings 460
 
 
c. Pores on halteres 461
 
 
Disposition of pores in other species 463
 
 
a. Pores on legs 464
 
 
b. Pores on wings 464
 
 
c. Pores on halteres * 464
 
 
d. Pores on abnormal species. . . ' 465
 
 
e. Generic, specific, individual, and sexual variations 468
 
 
Structure of pores in Musca domestica 471
 
 
a. External structure 471
 
 
b. Internal structure 473
 
 
Structure of pores in other species 478
 
 
a. External structure. 478
 
 
6. Internal structure 479
 
 
The antennal organs 481
 
 
Summary 482
 
 
Literature cited 484
 
 
INTRODUCTION AND METHODS
 
 
The results herein recorded are a continuation of the writer's investigation concerning the morphology of the olfactory pores. Up to date, including the present results, these organs have been carefully studied in Hymenoptera, Coleoptera, Lepidoptera, and Diptera. The chief object of the present investigation is to determine whether the olfactory pores are better adapted anatomically than the antennal organs to receive olfactory stimuli.
 
 
457
 
 
THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 29, NO. 5 OCTOBER, 1918
 
 
 
 
458 N. E. McINDOO
 
 
The investigators who have performed experiments on flies with mutilated antennae have concluded that these appendages bear the olfactory organs, regardless of whether or not the antennal organs are anatomically fitted to receive olfactory stimuU. Since these investigators failed to study sufficiently the behavior of the insects investigated, it is possible that the responses observed misled them in determining the seat of the olfactory organs.
 
 
In 1857 Hicks discovered porelike organs on the wings and halteres of flies, and claims that they are similar in structure and probably have the same function, that of smell. He was able to trace a nerve to each group of organs, the one going to the halter b^ing the larger. The same author ('59) found these organs in Hippobosca equina and Tipula olerocea, and in 1860 discovered them on the legs of various insects, including Diptera. In the same year Leydig described and figured the same organs on the halteres of Calliphora (Musca) vomitoria and Eristalis tenax. Each one of the foregoing authors was able to trace nerves to these pores, but they could not understand the internal anatomy of them.
 
 
Graber ('82) described and figured these organs on the wings and halteres of several Diptera, and called them chordotonal organs, because he thought the peripheral ends of the sense cells were sensory chords.
 
 
Lee ('85) described and figured in detail these structures on the halteres of Calliphora vomitoria, but he, like the preceding authors, failed to understand their internal anatomy.
 
 
The paper of Weinland ('90) is the most comprehensive one dealing with the sense organs found on the halteres, and as a whole it is the best, although he did not clearly understand the anatomy of these structures. He gives a good review of the hterature pertaining to the halteres, and according to him the earliest writers (beginning in 1711) said that these appendages served in maintaining the equilibrium of the insect while flying ; hence the Latin name, halteres and the English translation, balanciers. About a century later experiments proved that fhes with amputated halteres could fly, although not as well,
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 459
 
 
and consequently the preceding view has long since been abandoned. Another old view was that the halteres aid in respiration Hicks and Lee regarded the structures as olfactory organs, while Leydig and Graber thought they were auditory in function. Weinland detennined that the halteres in vibrating rapidly perform a number of different movements, and chiefly for this reason he thinks that the organs borne by them bring about the perception of movements, thereby steering the flight of the insect. He asserts that since the antennae bear the olfactory organs, the organs on the halteres certainly do not perform the same function.
 
 
Nagel ('94), in commenting on the probable function of the halteres, thinks that the first four preceding views have been abandoned, but he is a strong advocate of Weinland's view.
 
 
The paper of Prashad ('16) seems to be the most recent one concerning the sense organs on the halteres, and this author studied only the halteres of the mosquito, Ochlerotatus pseudotaeniatus Giles. He evidently did not have access to most of the literature on this subject and consequently has added little knowledge concerning these organs. He thinks that each organ has an external opening and fomid two scalpel groups of pores on each halter, while the present writer found only one scalpel group on each halter of mosquitoes belonging to other genera.
 
 
McEwen ('18) has just recently observed the sense organs on the wings of Drosophila ampelophila. He determined 'Hhat these organs had nothing to do with the response to light" (pp. 85 to 87), but performed no experiments using odor stimuli.
 
 
To obtain material for the study of the disposition of the olfactory pores', dried museum specimens were largely used. These specimens were obtained of Messrs. C. T. Greene and C. H. Popenoe through the courtesy of Dr. L. O. Howard. Mr. Greene is furthermore to be thanked for verifying the identification of all the species used. Fresh material was fixed in the modified Carnoy's fluid, and was embedded in celloidin and paraffin. The sections were cut three and five microns in thickness, and were stained in Ehrlich's hematoxylin and eosin. All the drawings were made by the writer and all are oiiginal except figures 50 to 55; these represent the antennal organs of flies
 
 
 
 
460 N. E. McINDOO
 
 
and mosquitoes, and were copied fi'om Hauser, vom Rath, and Nagel. The drawings were made at the base of the microscope with the aid of a camera lucida.
 
 
THE OLFACTORY PORES
 
 
Before making a study of the anatomy of the organs, called the olfactory pores by the writer ('14 a), the distribution and number of them were first investigated.
 
 
Disposition of pores in Musca domestica
 
 
Owing to an abundance of material and to the economic importance of the house fly, the olfactory pores of this insect have been studied and drawn in detail, and it is hoped that such work will encourage experimentation along practical lines.
 
 
a. Pores on legs. Seven groups of pores lie on each leg and the disposition of them is as follows: nos. 1 to 4 on the inner surface of the leg (fig. 1) arid nos. 5 to 7 on the outer surface; nos. 1, 2, and 5 being on the trochanter, nos. 3 and 6 on the femur, and nos. 4 and 7 on the tibia. Nos. 1 and 2, consisting of 5 and 8 pores, respectively, always lie on the anterior margin of the leg, while no. 3, composed of 11 pores, lies on the posterior margin. Nos. 4 and 7, when present, may lie on either or both margins of the leg and the number of pores in each group varies from one to three. No. 5, consisting of 3 pores, usually lies near the posterior margin, while no. 6, composed of 1 pore, lies near the anterior margin.
 
 
b. Pores on wings. Six groups and several scattered pores lie on each wing and the disposition of them is as follows : Nos. 8 to 1 1 and scattered pores a to c lie on the dorsal surface of the wing (fig. 2), while nos. 12 and 13 and the scattered pores d and e lie on the ventral surface. No. 8, consisting of about 24 pores, lies at the proximal end of the propterygium (P7-), while nos. 9 to 13 lie on the subcostal {Sc) vein in about the positions as indicated by the numbers in figure 2. The number of pores *in each of these groups varies slightly, but the average number in each is about as follows: no. 9 has 50 pores; no. 10, 12 pores; no. 11, 10 pores;
 
 
 
 
THE OLFACTOKY ORGANS OF DIPTERA
 
 
 
 
461
 
 
 
 
No. 12, 9 pores, and no. 13, 18 pores. The scattered pores varyconsiderably in number and position and they are located about as follows: 1 at a on the base of the humeral vein; 2 always present at h on the distal end of the first radial vein ; 1 at c on the radiomedial vein; 1 at c? on the proximal end of the first radial vein; and 1 at e on the fourth radial vein.
 
 
 
 
 
Fig. 1 Portions of legs of house fly (Musca domestica cf), showing location of groups nos. 1 to 7 of olfactory pores. The drawings at the right rcTpresent the inner surface and those at the left the outer surface. AntM and PoslM stand for anterior and posterior .margins. X 20.
 
 
 
 
c. Pores on halteres. Five groups and 1 isolated pore lie on the. base of each halter (fig. 3) ; nos. 14 to 16 and the isolated pore at / being found on the dorsal surface and nos. 17 and 18 on the ventral surface. The pores lie on plates whose outlines are similar in shape to the contours of the groups of pores themselves;
 
 
 
 
462
 
 
 
 
N. E. McINDOO
 
 
 
 
hence, the pores in nos. 14 and 18 have been called scalpel organs because each group lies on a plate shaped like a scalpel. No. 15 lies on the basal plate, consequently its pores have been called basal organs. No. 16 lies on the anterior end of the basal plate, while no. 17 on the opposite side of the halter lies on the proximal end of the scalpel plate; the pores in these two groups are like in structure, and since their structure is like that of those on the wings they have been called Hicks' organs. In the following pages it is shown that the scalpel and basal organs are unlike in structure and also neither one of these two types is exactly like the Hicks' organs. The isolated pore at / is found on only about
 
 
 
 
 
Fig. 2 Portion of left wing of Musca domestica cf , showing location of groups nos. 8 to 13 of olfactory pores on propterygium (Pr) and on subcostal vein (Sc) and the scattered pores at points marked a to e. The drawing at the left represents the dorsal surface and the one at the right the ventral surface. X 20.
 
 
 
 
one-half of the halteres of the house fly, and it has been called an undetermined type by Weinland.
 
 
Considering the twenty halteres belonging to five males and five females, the numbers of pores in the groups are as follows: In no. 14 they vary from 74 to 110 with 92 as an average; in no. 15, from 70 to 96 with 88 as an average; in no. 16, from 10 to 11 with almost 11 as an average; in no. 17, from 3 to 8 with 7 as an average, and in no. 18, from 74 to 110 with 93 as an average.
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
 
 
463
 
 
 
 
Disposition of pores in other species
 
 
In making a comparative study of the disposition of the olfactory pores in Diptera, 47 species, belonging to 38 genera and representing 21 families, were used. In most cases only one specimen of each species was employed, and whenever a portion of an appendage or an entire appendage was missing or was badly mutilated in being prepared for study, the supposed number
 
 
 
 
 
Fig. 3 Right halter of Miisca domestica cf, showing location of scalpel pores (nos. 14 and 18), basal pores (no. 15), Hicks' pores (nos. 16 and 17) and the undetermined type (/). The upper drawing represents the dorsal surface and the lower one the ventral surface. The upper margin of each drawing represents the anterior surface and the lower margin the posterior surface. F, one of the folds caused during preparation of halter. X 100.
 
 
 
 
of pores on this portion or entire appendage was regarded the same as the number found on the corresponding portion or entire appendage on the opposite side of the body. Since the pores on only one specimen for each species were counted, the total number of pores recorded cannot be a fair average. Besides this error, there is also another small probable error for each species, because a few of the pores were probably overlooked, and often, as on the tibiae, it was impossible to distinguish the
 
 
 
 
464 N. E. McINDOO
 
 
olfactory pores from hair sockets. As a rule, only the legs, wings, and halteres were examined, although in several instances the chitinous parts of the reproductive organs and the mouth parts were also examined, but usually no olfactory pores were seen on them. The sex of the species, except in a few cases, was not determined.
 
 
a. Pores on legs. The disposition of the pores on the legs is more similar to that of those on the legs of Hymenoptera (McIndoo, '14 b) than to those on the legs of Lepidoptera or Coleoptera (Mclndoo, '15, '17). Pores were found on each trochanter and femur examined, but sometmies none was seen on a tibia and not one was ever observed on a tarsus. The distribution of them is similar to that of the house fly, already described. The total number of them varies considerably, depending on the number of groups present and the size of the species. The groups are usually conspicuous and the one on the femur is quite characteristic ; it consists of two or three rows of pores variously arranged, depending on the genus examined.
 
 
h. Pores on wings. The disposition of the pores on the wings is more similar to that of those on the wings of Lepidoptera than to those on the wings of Hymenoptera or Coleoptera. In Lepidoptera the pores are well grouped, while in Diptera they are poorly grouped and consequently not much reliance can be placed upon the number of groups recorded; for this reason the variation in the number of groups need not be discussed. Lepidoptera have more isolated pores than have Diptera, and in the former order they may extend along the full length of the veins, while in Diptera they are never found farther than two-thirds the distance from the base of the wing. The propterygium (fig. 2, Pr.) was often lost during the preparation of the integument, but group No. 8, was usually found on it whenever this part of the wing was present. This is the first time for this group to be reported.
 
 
c. Pores on halteres. As already mentioned on page 462, there are four types of pores on the halteres, although the undeterminde type, consisting of large isolated pores, should be called isolated Hicks' pores. The groups of Hicks' pores are seen only with
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 465
 
 
much difficulty and doubtless many of them were overlooked. The writer is the only observer who has seen a group of them on either side of the halter. Since the number of pores on the halteres has never been tabulated, the following table is presented. A reference to this table will show the minor variations in these pores better than a description of them, therefore only the more important variations need be pointed out. The Hicks' groups were found on 75 per cent of the halteres; a basal group on each halter, except in one species (no. 2) ; one or two scalpel groups on each halter; and the undetermined pores on 45 per cent of the halteres examined. One basal group (excepting no. 2) was invariably present on each halter, while two scalpel groups were observed on each halter examined, except in the three mosquitoes (nos. 3 to 5) and two of the wingless forms (nos. 13 and 48); only one scalpel group was seen on each halter of these five species.
 
 
d. Pores on abnormal species. To determine what effect environmental conditions has had upon the disposition of the olfactory pores, seven species were selected for this purpose. Table 3 (p. 470) shows to what families they belong and the number of their olfactory pores in comparison with the pores of the normal species. In table 2 they are arranged according to the degree of degeneracy of the wings and halteres and they shall be described accordingly.
 
 
The sheep tick (45 Melophagus ovinus) is much compressed; has no signs of wings and halteres; its legs are short and the segments are wide; the entire integument is thick and tough. Olfactory pores were found only on the trochanters and femora; their distribution is normal, but their number is reduced. The bat tick (48 Nycteribia bellardii) is also much compressed and has no compound eyes; its wings are totally wanting and its halteres are unusually small. The disposition of the pores on its legs is normal, but on the halteres the pores are comparatively few; the scalpel type being reduced to only one group per halter (table 1). The so-called wingless female of the snow-fly (2 Chionea valga) copulates on the surface of the snow and it seems to be abnormal in four ways; 1) The number of pores on
 
 
 
 
466
 
 
 
 
N. E. McINDOO
 
 
 
 
TABLE 1
 
 
 
 
Number of organs in the four types of olfactory pores found on the halteres of
 
 
Diptera
 
 
 
 
NUMBER AND NAMES OF SPECIES
 
 
 
 
1. Tipula sp
 
 
2. Chionea valga 9
 
 
3. Culex pipiens
 
 
4. Aedes vexans '
 
 
5. Corethra cinctipes
 
 
6. Mycetophila punctata. . . .
 
 
7. Sciaria inconstans
 
 
8. Macrosargus decorus
 
 
9. Tachydromia sp
 
 
10. Rhamphomyia abdita
 
 
11. Psilopus sp
 
 
12. Aphiochaeta sp
 
 
13. Pulicifora borinquensis 9
 
 
14. Calobata antennipes
 
 
15. Piophila casei
 
 
16. Tritoxa flexa
 
 
17. Anacampta latiuscuta. . . .
 
 
18. Euxesta notata
 
 
19. Dacus cucurbitae
 
 
20. Milichiella lacteipennis. . .
 
 
21. Drosophila busckii
 
 
22. Drosophila amoena
 
 
23. Drosophila f unebris
 
 
24. Paralimna decipier
 
 
25. Paralimna appendiculata.
 
 
26. Ephydra gracilis
 
 
27. Chlorops coxendix
 
 
28. Tetanocera plumos
 
 
29. Helomyza tincta
 
 
30. Scatophaga stercoraria. . .
 
 
31. Scatophaga furcata ' . .
 
 
32. Homalomyia canicularis. .
 
 
33. Hylemyia simpla
 
 
34. Phorhia brassicae
 
 
35. Phorbia fussiceps
 
 
36. Coenosia sp
 
 
 
Nos. 15 and 17
 
 
Hicks'
 
 
 
 
Number of groups
 
 
 
 
Number of pores
 
 
 
 
Number of groups
 
 
 
 
10
 
 
45
 
 
6
 
 
20
 
 
 
 
10 18 16 34 12 14 20
 
 
12 12
 
 
4
 
 
4
 
 
12
 
 
36 22 18 22 20 24 39 22 16
 
 
 
 
No. 15 Basal
 
 
 
 
Number of pores
 
 
 
 
Number of groups
 
 
 
 
90 130
 
 
156 160 158 140 272
 
 
72 152 130
 
 
65
 
 
64 128 140
 
 
65 138 145 168 140 108 100 108
 
 
96 120 100
 
 
74 194 160 150 150 166 166 144 140 140
 
 
 
 
Nos.
 
 
14 and 18
 
 
Scalpel
 
 
 
 
Number of pores
 
 
 
 
Num her of pores
 
 
 
 
134 26 152 138 132 189 176 552 200 384 438 209 72 292 231 191 307 277 332 311 180 212 236 209 216 192 182 358 340 302 300 306 276 319 340 248
 
 
 
 
Total Number of pores
 
 
 
 
230 28 286 298 298 350 330 870 282 536 588 278 140 430 389 272 485 434 514 471 288 324 358 309 342 306 256 588 522 470 472 492 466 502 502 404
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
 
 
467
 
 
 
 
TABLE 1— Continued
 
 
 
 
NUMBER AND NAMES OF SPECIES
 
 
 
 
37. Musca domestica cf
 
 
38. Musca domestica 9
 
 
39. Sarcophaga plinthopyga
 
 
40. Sarcophaga lambens
 
 
41. Sarcophaga helicis
 
 
42. Sarcophaga sp
 
 
43. Sarcophaga sp
 
 
44. Olfersia americana cf ' . .
 
 
45. Melophagus oviniis 9
 
 
46. Lipoptena depressa d' ..'... .
 
 
47. Hippobosca struthinionis cT
 
 
48. Nycteribia bellardii cf
 
 
 
 
Variation.
 
 
 
 
'Nos.
 
 
15 and 17
 
 
Hicks'
 
 
 
 
Number of groups
 
 
 
 
0 4
 
 
 
 
Number of pores
 
 
 
 
35 35 18 32 48 36 34
 
 
 
 
10 16
 
 
 
 
0 48
 
 
 
 
No. 15 Basal
 
 
 
 
Number of groups
 
 
 
 
Number of pores
 
 
 
 
183 166 140 '168 186 146 150 60
 
 
68
 
 
120
 
 
6
 
 
 
 
0272
 
 
 
 
Nos.
 
 
14 and 18
 
 
Scalpel
 
 
 
 
Number of groups
 
 
 
 
24
 
 
 
 
Number of pores
 
 
 
 
387 350 316 334 326 292 334 242
 
 
122
 
 
304
 
 
36
 
 
 
 
26552
 
 
 
 
Number of pores
 
 
 
 
Total number of pores
 
 
 
 
606 552 ^74 534 564 474 518 304
 
 
200
 
 
442
 
 
44
 
 
 
 
28870
 
 
 
These numbers refer to those in figure 3, showing the same types on the halteres of the house fly.
 
 
t Halteres totally wanting.
 
 
 
 
the legs is slightly more than might be expected; 2) the wing is nothing more than a little pad, about as long as the base of the halter, but it bears no pores; 3) the halteres seem normal in size, but the pores on them are comparatively few in number, the Hicks' and basal groups being absent; 4) the ovipositor seems to bear 21 small pores, but they are not recorded in the tables. The chitinous parts of the genital organs of all the abnormal species and of a few of the normal species were examined, but no oKactory pores were observed on them except as above stated. The sorcalled wingless female phorid (13 Pulicifora borinquensis) is the smallest specimen examined. The wing is padlike, about the size of the halter and it bears 7 pores. The number of pores on the halter appears to be reduced. The deer tick (46 Lipoptena depressa) has vestigial wings which are unusually thick
 
 
 
 
468
 
 
 
 
N. E. McINDOO
 
 
 
 
at the base. The number of pores on them is greatly reduced. The two remaining parasitic species, the fowl tick (44 Olfersia americana) and the ostrich tick (47 Hippobosca struthinionis) , are winged and apparently are normal, unless one considers the number of their pores slightly reduced.
 
 
TABLE 2 Number of olfactory pores found on abnormal species
 
 
 
 
NUMBER AND NAME OF SPECIES
 
 
 
NUMBER OF PORES ON
 
 
 
Total number of
 
 
 
 
 
Legs
 
 
 
Wings
 
 
 
Hal teres
 
 
 
pores
 
 
 
45. Melophagus ovinus 9
 
 
48. Nycteribia bellardii o^
 
 
2 Chionea valga 9
 
 
 
162 178 .391 168 144 168 180
 
 
 
A
 
 
A
 
 
B
 
 
C14
 
 
D75
 
 
154
 
 
167
 
 
 
E F44
 
 
28 140 200 304 442
 
 
 
162 222
 
 
419
 
 
 
13 Pulicifora borinquensis 9
 
 
 
322
 
 
 
46 Lipoptena depressa d^
 
 
 
419
 
 
 
44. Olfersia americana cf '
 
 
47. Hippobosca struthinionis cf
 
 
 
626
 
 
789
 
 
 
Variation <
 
 
 
144391
 
 
 
00167
 
 
 
00442
 
 
 
162 789
 
 
 
 
The following is an explanation of letters A to F in the above table : A, totallywingless; B, wing about as long as base of halter; C, wing about size of halter; D, wing much reduced, about same length as that of the short tarsus; E, halteres totally wanting; and F, halteres unusually small and peduncles threadlike.
 
 
e. Generic, specific, individual, and sexual variations. As already stated, the variations between the olfactory pores of Hymenoptera, Coleoptera, Lepidoptera, and Diptera are large and in regard to both disposition and structure of the pores they are characteristic for each order. The variations among the families depend upon the families compared; for example, the disposition of the pores in Tipulidae and Muscidae is very different, but in Muscidae and Sarcophagidae only slightly different. The generic characteristics are slight variations in the disposition of the pores, while the specific variations are based almost solely upon the total number of pores present. The individual and sexual variations are distinguishable only by comparing the total number of pores present.
 
 
A reference to tables 1 and 3 shows that the variations found pertain to the number of groups on the halteres and to the variations in number of pores on the legs, wings, and halteres. Exclud
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 469
 
 
ing the wingless forms (nos. 13 and 48), the mosquitoes (nos. 3 to 5) differ from all the other Diptera examined in that each halter bears only one scalpel group instead of two. While the legs and wings of these mosquitoes are long and slender, the halteres are short and stout; relative to the other species examined, the reverse is generally true. The number of pores on the halteres of mosquitoes is considerably less than the average number on the halteres of flies, but they appear to be considerably larger. Tipulidae is the only family which bears more pores on the legs than on either the wings or halteres. As a rule, the smaller species bear fewer pores than the larger ones, but there are many exceptions; for example, Tritoxa flexa (no. 16) is one of the largest specimens examined, yet its total number of pores is among the lowest recorded. Among the genera the total number of pores may vary slightly, as in the mosquitoes (nos. 3 to 5) and in Anthomyidae, or considerably, as in Mycetophilidae and Empididae; but among the species the total number usually varies only slightly, as in nos. 24 and 25, 30 and 31, 34 and 35,' but occasionally a larger variation may be found, as in nos. 21 to 23 and 39 to 43.
 
 
The olfactory pores on five females and five males of Musca domestica were carefully counted to determine the individual and sexua^ variations. For the females the number of pores on the legs vary from 165 to 175 with 186 as an average; on the wings, from 219 to 274 with 252 as an average; on the halteres, from 530 to 570 with 552 as an average. For the males the number of pores on the legs vary from 168 to 180 with 172 as an average; on the wings, from 232 to 257 with 248 as an average; on the halteres, from 564 to 625 with 606 as an average. Thus, as an average a female bears 972 pores and a male 1026 pores.
 
 
The mouth parts and antennae of many specimens were examined, but no olfactory pores were seen on them. Other parts of the integuments besides those discussed were also often examined, although no olfactory pores were found on them, except on the ovipositor already mentioned (p. 467) and occasionally two or three pores on the thorax near the base of the wing. These were not carefully recorded and do not appear in the tables.
 
 
 
 
470
 
 
 
 
N. E. McINDOO
 
 
 
 
TABLE 3 Number of olfactory pores on legs, wings, and halteres of Diptera
 
 
 
 
Tipulidae. Culicidae.
 
 
 
 
Mycetophilidae . <
 
 
Stratiomyidae
 
 
Empididae X
 
 
Dolichopodidae. . . Phoridae <
 
 
Micropezidae
 
 
Sepsidae
 
 
f Ortalidae <
 
 
Agromvzidae
 
 
f Drosophilidae.. . -j
 
 
f Ephydridae
 
 
Chloropidae
 
 
Sciomyzidae . . . Helomyzidae. .
 
 
Scatophagidae . Anthomyidae . . Muscidae
 
 
 
 
NUMBER AND NAME OF SPECIES
 
 
 
 
1. Tipula sp
 
 
2. Chionea valga 9 Harr
 
 
3. Culex pipiens L
 
 
4. Aedes vexans Meig
 
 
5. Corethra cinctipes Coq
 
 
6. Mycetophila punctata Meig..
 
 
7. Sciaria inconstans Fitch
 
 
8. Macrosargus decorus Say
 
 
9. Tachydromia sp
 
 
10. Rhamphomyia abdita Coq.. . .
 
 
11. Psilopus sp
 
 
12. Aphiochaeta sp
 
 
13. Pulicifora boringuensis 9 Wheeler
 
 
14. Calobata antennipes Say
 
 
15. Piophila casei L
 
 
16. Tritoxa flexa Wied
 
 
17. Anacampta latiuscuta Loew. . .
 
 
18. Euxesta notata Wied
 
 
19. Dacus cucurbitae Coq
 
 
20. Milichiella lacteipennis Loew. .
 
 
21 . Drosophila busckii Coq
 
 
22. Drosophila amoena Loew
 
 
23. Drosophila funebris Fabr
 
 
24. Paralimna decipier Loew
 
 
25. Paralimna appendiculata Loew
 
 
26. Ephydra gracilis Pack
 
 
27. Chlorops coxendix Fitch
 
 
28. Tetanocera plumos Loew
 
 
29. Helomyza tincta Walk
 
 
30. Scatophaga stercoraria L
 
 
31. Scatophaga surcata Say
 
 
32. Homalomyia canicularis L
 
 
33. Hylemyia simpla Coq
 
 
34. Phorbia brassicae Bouche
 
 
35. Phorbia fussiceps Zett
 
 
36. Coenosia sp
 
 
37. Musca domestica cf L
 
 
38. Musca domestica 9 L
 
 
 
 
NDMBEB OF PORES |
 
 
 
 
 
ON
 
 
 
 
 
Legs
 
 
 
Wings
 
 
 
Halteres
 
 
 
380
 
 
 
252
 
 
 
230
 
 
 
391
 
 
 
B*
 
 
 
28
 
 
 
208
 
 
 
170
 
 
 
286
 
 
 
194
 
 
 
192
 
 
 
298
 
 
 
220
 
 
 
160
 
 
 
298
 
 
 
225
 
 
 
343
 
 
 
350
 
 
 
160
 
 
 
138
 
 
 
330
 
 
 
272
 
 
 
408
 
 
 
870
 
 
 
186
 
 
 
60
 
 
 
282
 
 
 
148
 
 
 
192
 
 
 
536
 
 
 
168
 
 
 
163
 
 
 
588
 
 
 
159
 
 
 
74
 
 
 
278
 
 
 
168
 
 
 
C14
 
 
 
140
 
 
 
138
 
 
 
161
 
 
 
430
 
 
 
124
 
 
 
154
 
 
 
389
 
 
 
90
 
 
 
111
 
 
 
272
 
 
 
151
 
 
 
222
 
 
 
485
 
 
 
166
 
 
 
184
 
 
 
434
 
 
 
182
 
 
 
192
 
 
 
514
 
 
 
128
 
 
 
124
 
 
 
471
 
 
 
160
 
 
 
98
 
 
 
288
 
 
 
173
 
 
 
110
 
 
 
324
 
 
 
180
 
 
 
117
 
 
 
358
 
 
 
168
 
 
 
138
 
 
 
309
 
 
 
173
 
 
 
126
 
 
 
342
 
 
 
164
 
 
 
183
 
 
 
306
 
 
 
177
 
 
 
138
 
 
 
256
 
 
 
174
 
 
 
202
 
 
 
588
 
 
 
172
 
 
 
197
 
 
 
522
 
 
 
170
 
 
 
214
 
 
 
470
 
 
 
173
 
 
 
208
 
 
 
472
 
 
 
195
 
 
 
198
 
 
 
492
 
 
 
178
 
 
 
241
 
 
 
466
 
 
 
174
 
 
 
236
 
 
 
502
 
 
 
177
 
 
 
240
 
 
 
502
 
 
 
178
 
 
 
223
 
 
 
404
 
 
 
172
 
 
 
248
 
 
 
606
 
 
 
168
 
 
 
252
 
 
 
552
 
 
 
 
Total number of pores
 
 
 
 
862 419 664 684 678 918 628
 
 
1550 528 876 919 511 322 729 667 473 858 784 888 723 546 607 655 615 641 653 571 964 891 854 853 885 885 912 919 805
 
 
1026 972
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
 
 
471
 
 
 
 
TABLE 3— Continued
 
 
 
 
Sarcophagidae . . ^
 
 
Hippoboscidae. . <
 
 
I Nycteribiidae. ...
 
 
 
 
NUMBER AND NAME OF SPECIES
 
 
 
 
39. Sarcophaga plinthopyga Wied...
 
 
40. Sarcophaga lambens Wied..." ....
 
 
41. Sarcophaga helicis Towns ' . .
 
 
42. Sarcophaga sp
 
 
43. Sarcophaga sp
 
 
44. Olfersia americana cf Leach. . . .
 
 
45. Melophagus ovinus 9 L
 
 
46. Lipoptena depressa cf Say
 
 
47. Hippoboscastruthinionis cf Jansen
 
 
48. Nycteribia bellardii cf Rondani..
 
 
 
 
Variation
 
 
 
 
NUMBER OP PORES ON
 
 
 
 
Leg8 Wings Hal
 
 
 
174 170 179 180
 
 
 
 
198 204 218 194
 
 
 
 
186 : 202
 
 
 
 
168 162 144 180
 
 
178
 
 
 
 
154
 
 
A
 
 
D75 167
 
 
A
 
 
 
 
90391
 
 
 
 
00 408
 
 
 
 
474 534 564 474 518 304 E 200 442 F44
 
 
 
 
00 871
 
 
 
 
Total number of pores
 
 
 
 
908 961 848 906 626 162 419 789 222
 
 
 
 
1621550
 
 
 
For explanation of letters A to F, see p. 468. Structure of pores in Musca domestica
 
 
The preceding pages deal with the disposition of the olfactorypores, and now a discussion of their anatomy will be given.
 
 
a. External structure. As already stated, the pores in groups nos. 16 and 17 on the halteres (fig. 3) have been called Hicks' organs, and since their structure is like that of those on the legs and wings, all of these pores may be regarded as belonging to the Hicks' type. Since their anatomy does not differ materially from that of those in the other orders of insects, discussed in other papers by the wTiter, a reference to figures 4 to 15 may suffice at this place.
 
 
Under a high-power lens the scalpel groups (nos. 14 and 18) and the basal group (no. 15) look somewhat as shown in figures 16 and 17. They may be compared with the Hicks' type (nos. 16 and 17). It is to be noted that the scalpel group no. 14 consists of 11 rows and no. 18 of 10 rows. From a superficial view the rows appear to be flat, but sections will show that the pores are linked together and stand in ridges, projecting far above the surrounding integument. The summit of each ridge is beautifully sculptured, and' a row of stout hairs (fig. 16, Hr^)
 
 
 
 
472
 
 
 
 
N, E. McINDOO
 
 
 
 
arises between each two rows of pores. These rows of hairs are only prolongations of the chitin and therefore should be called pseudohairs; their only function is probably to protect the rows of pores. The apertures (PorAp) of the pores are invariably long, narrow slits, while sculptured markings replace the pore walls and pore borders in the Hicks' tjrpe. The two halves
 
 
 
 
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Figs. 4 to 15 External view of olfactory pores in Musca domestica cf , showing variation in size. Fig. 4, groups nos. 1 and 2 (fig. 1); fig. 5, group no. 3; fig. 6, group no. 4; fig. 7, group no. 5; fig. 8, group no. 6; fig. 9, group no. 8 (fig. 2) ; fig. 10, group no. 9; fig. 11, 10 of 12 pores in group no. 10; fig. 12, 9 of 10 pores in group no. 11; fig. 13, group no. 12; fig. 14, 6 of 18 pores in group no. 13; fig. 15, scattered pores at 6. X 500.
 
 
 
 
{PorR), surrounding the aperture, are similar in position to the pore wall, but do not correspond to it; this structure may be called the pore ridge. The portion, marked PorL, may be called the pore link, because it unites the pore ridges; in position it is similar to the pore border, but it is quite different in structure.
 
 
The structure of the basal type of pores is similar to that of the Hicks' type, excepting pore borders are not present and a row of
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 473
 
 
pseudohairs arises between each two rows of pores. Each basal group consists of about eight rows of pores which are usually smaller than the scalpel pores; the pseudohairs in this group are also smaller than those in the scalpel group. The Hicks' pores are never protected by pseudohairs.
 
 
 
 
 
Figs. 16 and 17 External view of scalpel pores (nos. 14 and 18), basal pores (no. 15), Hicks' pores (nos. 16 and 17), and the undetermined type (/) on base of right halter of Musca domestica cf (fig. 3). All of the pseudohairs (Hr^) in group no. 15 are represented, but only a few of those in groups nos. 14 and 18 are shown, the bases of the remainder being represented by black dots. X 500.
 
 
b. Internal structure. As in Lepidoptera, the olfactory pores of Diptera may be called dome-shaped structures. All of the pores on the legs (fig. 18) and most of those on the wings (fig. 19) are typical dome-shaped structures, while the remainder on the wings (figs. 20 and 21) and all of those on the halteres (figs. 23 to 27) are modifications of the typical structure. It will be noted that the internal structure of each type of pore is identical to that of any other type and it is also similar to that of the
 
 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 5
 
 
 
 
474
 
 
 
 
N. E. McINDOO
 
 
 
 
olfactory pores in other orders of insects; therefore, it is the external structure that really determines the various types.
 
 
A hypodermal strand (figs. 23, 26, and 28, HypS), running from the hypodermis (fig. 25, Hyp) to the chitinous cone (fig. 26; Co7i), is always present. In this strand may be observed the
 
 
 
 
 
 
 
20
 
 
 
 
21
 
 
 
 
24
 
 
 
 
 
 
27
 
 
 
 
 
J'
 
 
 
 
25 ^
 
 
Figs. 18 to 28 Sections showing internal anatomy of olfactory pores of Musca domestica. Fig. 18, from trochanter; figs. 19 to 21, 3 variations on wing; fig. 22, portion of cross-section of wing (X 500); fig. 23, largest Hicks' pores; fig. 24, smallest, and fig. 25, largest basal pores, both rows being cut lengthwise; fig. 26, 4 rows of largest scalpel pores cut crosswise and 1 cut lengthwise; fig. 27, a row of smallest scalpel pores cut lengthwise; and fig. 28, from an oblique section of a scalpel row of pores, only their external view and nervous connection having been drawn. The sense fiber (SF) and hypodermal strand (HypS) are taken from a deeper focus. Attention is called to the sense fiber ending at the center of thepore aperture. Con, chitinous cone ; Hr^, pseudohair ; Hyp, hypodermis ; A'^, nerve ; PorAp, pore aperture; PorL, pore link; PorR, pore ridge; SC, sense cell, and Tr, trachea. X 1000.
 
 
 
 
sense fiber (figs. 23, 25, and 28, SF), but it is easily overlooked owing to the minute size of these organs. The sense cells in the legs and wings (fig. 22, SC) are spindle-shaped as usual, but in the halteres (fig. 25, SC) they are more than spindle-shaped and assume almost a spherical shape (fig. 29, SC). A pore aperture (figs. 19 and 26, PorAp) was seen only occasionally
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 475
 
 
and then never distinctly; it would never have been regarded as an opening had not the writer seen many good examples of it in the olfactory pores of other insects. These pores are the smallest ones ever examined by the writer, and this fact easily explains why other observers have never seen the pore apertures. The sections were studied under a magnification of 1900 diameters, and with the aid of a camera lucida the drawings made represent a magnification of 3000 diameters before reduction; and they were reduced to 1000 diameters.
 
 
As already stated, the pores on the legs, wings and groups nos. 16 and 17 on the halteres belong to the Hicks' type, while group no. 15 belongs to the basal type and nos. 14 and 18 to the scalpel type. A glance at figures 19 to 25 shows that the structure of the basal type (figs. 24 and 25) is like that of the Hicks' type (figs. 20 and 23), and the only difference (not shown in these figures) between these two types is that a row of pseudohairs (fig. 16) lies between each two rows of pores in the basal group. Pseudohairs (figs. 19 and 20, Hr'^) also protect some of the pores on the wings, but they are never arranged in rows as they are on the halteres.
 
 
The size of the pores in any type varies considerably. This is shown by comparing the smallest and largest basal pores (figs. 24 and 25) and the largest and smallest scalpel pores (figs. 26 and 27). The scalpel type differs from the other types in the following three particulars: 1) The domes lie totally above the surrounding chitin; 2) the bottoms of the domes are considerably constricted, while in the basal and Hicks' types on the halteres the domes are projected about one-half their height above the surrounding integument and their bases are constricted little or not at all, and 3) the tops of the domes are beautifully sculptured and assume a more or less flat surface. One pore (fig. 21) on the wing, resembling a scalpel pore, was found, while several (fig, 20) on the wing are identical to those in the Hicks' and basal groups on the halteres.
 
 
Sections passing longitudinally through the rows of basal pores show the pores as drawn in figures 25 and 29 {BPori), while sections passing transversely through the rows show the pores as
 
 
 
 
476
 
 
 
 
N. E. McINDOO
 
 
 
 
drawn in figure 29 (BPoro). Figure 26 represents a section passing transversely through four rows and longitudinally through one row of scalpel pores. In the latter pore, as well as in figures 27, 28, and 29 (SPori), the pore ri'dge (PorR) and pore link (PorL) can be identified. Figure 29 represents an oblique longitudinal section through the base of the halter in the direction of A A in figure 3. The large nerve (A') is very conspicuous; it spreads out fanlike and connects with the masses of sense cells
 
 
 
 
 
Fig. 29 Longitudinal section (| diagrammatic), cut in direction of line AA in figure 3, through base of halter of Musca domestica, showing internal anatomy, scalpel pores (nos. 14 and 18), basal pores (no. 15) and Hicks' pores (no. 16). The chordotonal organ (ChO) is only in its approximate position and was copied from Lee ('85). One row each of basal pores (BPovi) and scalpel pores {SPovi) cut lengthwise, and 3 rows of basal pores (BPor-i) and 5 rows of scalpel pores (no. 18) were cut crosswise. Ch, internal view of chitin; Ch-2, external view of chitin; M, muscle; A, nerve; 5C, sense cell, and Tr, trachea. X 500.
 
 
 
 
(SC). A trachea (Tr), muscles (M) and a chordotonal organ (ChO) are also present. Both Lee and Weinland have studied the chorodotonal organ, but the present writer has paid little attention to it, hoping later to make a special study of this type of sense organ. In figure 29 it is represented in only its approximate position as drawn by Lee.
 
 
Figures 30 and 31 are schematic drawings of a portion of a row in a scalpel group, showing the pores both in perspective and in
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
 
 
477
 
 
 
 
section. In figure 30 the row was cut crosswise, passing longitudinally through the slitlike aperture, whereas in figure 31 the row was cut lengthwise, passing transversely through the slitlike aperture.
 
 
Figure 32 is a drawing, showing a portion of the base of the halter in perspective and in section, it was cut crosswise in the direction of line BB in figure 3. The muscle (M) and chordotonal organ (ChO) are drawn in only their approximate positions as represented by Weinland; their points of attachments are incorrect. The scalpel pores (nos. 14 and 18) and a few basal pores (no. 15), shown both in perspective and in section, lie on
 
 
 
 
 
Figs. 30 an^ 31 Schematic drawings of a portion of a scalpel row on halter of Musca domestica, showing the row in perspective and in section. In figure 30, the row was cut crosswise, longitudinally through the slitlike aperture, while in figure 31 thfe row was cut lengthwise. The nerve (A^) is drawn in perspective, and strong pseudohairs (Hr^) bend over the pores, protecting them well.
 
 
curved plates, and it is noted that the surface of the base of the halter is very rough, being made up of minute hills and hollows. In Weinland's drawings it is noted that the nerve does not run beyond the olfactory pores on the halter, but the trachea runs into the peduncle and stops there. A cross-section of the knob of a halter somewhat resembles a double convex lens ; it contains masses of cells which are certainly not sensory, but probably they are the remains of the early hypodermis. The surfaces of the knobs of prepared halteres bear a few true hairs, and they are generally smooth excepting the folds (fig. 3, F), caused by preparing the specimens.
 
 
 
 
478
 
 
 
 
N. E. McINDOO
 
 
Structure of pores in other species
 
 
 
 
Since the structure of the pores in the house fly has been described in detail, only the more important variations concerning the structure of the pores in other Diptera will be mentioned and attention will be called to the various figures.
 
 
a. External structure. On the legs of one or two specimens the pore walls are diamond-shaped instead of being round and oblong,
 
 
 
 
 
Fig. 32 Portion of base of right halter of Musca domestica, cut across in direction of line BB in figure 3, showing halter, scalpel pores (nos. 14 and 18), and §7 basal pores (no. 15) in perspective and in section. The chordotonal organ (ChO) and muscle (M) were copied from Weinland ('90) and were drawn in only their approximate positions.
 
 
and the pore apertures in several instances are long, more or less slit-shaped, and resemble the slits in the lyriform organs of spiders (Mclndoo, '11); such is particularly true on the trochanters of Tipula (fig. 33). The pores on the tibiae of Sarcophaga (fig. 34) are very large and striking. The pore wall is surrounded by three areas of differently colored chitin; the inner one is real light in color; the middle one is a little darker, and the outer one, having a soft appearance, is still darker.
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 479
 
 
b. Internal structure. A reference to figures 35 to 49 shows that the size of the pores usually varies according to the size of the insect studied; thus the average size of the pores in the robber fly (figs. 39 to 43) is greater than that of the pores in the flesh fly (fi-gs. 44 to 49), although the pores on the halters of both flies are about equal in size. WTiile the pores on the legs are always dome-shaped, many of those on the wings (figs. 42 and 46) and a few on the halteres (fig. 47) are not dome-shaped. Many of those on the wings (fig. 45) of Sarcophaga project far above the surrounding chitin and their tops slightly resemble those of the scalpel pores on the halteres. A study of these pores shows a complete series of variations, ranging from the Hicks' type to the scalpel type, and perhaps each type is still in the trans
 
 
 
 
54
 
 
Figs. 33 and 34 External views of olfactory pores of other flies. Fig. 33, a group from trochanter of Tipula, showing slitlike pore apertures, and fig. 34, a group from tibia of Sarcophaga plinthopyga, showing 3 areas of chitin around pore wall. X 500.
 
 
itional stage. Morphologically the scalpel type is the most highly developed, but physiologically it is probably little or no better developed than any other type of pores.
 
 
All of these results indicate that while the hind wings of Diptera have been gradually reduced in size, consequently gradually diminishing their fljing ability, their sensory function has been greatly increased, and now they bear the highest type of olfactory pore yet found. The latter statement is supported by the fact that in Hymenoptera, the hind wings bear about onehalf as many pores as do the front wings; in Lepidoptera the hind wings do not bear quite as many pores as do the front wings, while in Diptera the halteres bear about as many pores as do the wings and legs combined, or close to one-half the total number of pores found.
 
 
 
 
480
 
 
 
 
N. E. McINDOO
 
 
 
 
 
Figs. 35 to 49 Sections showing variations in internal anatomy of olfactory pores of other flies. Figs. 35 to 38, from crane fly (Brachypremna dispellens Walk.); fig. 35, from trochanter; fig. 36, from wing; and figs. 37 and 38, from halter, fig. 37 being basal type and fig. 38 being scalpel type. Figs. 39 to 43, from robber fly (Erax asstuans L.); fig. 39, from trochanter; fig. 40, from femur; figs. 41 and 42, from wing, and fig. 43, scalpel type from halter. Figs. 44 to 49, from flesh fly (Sarcophaga sp.); fig. 44, from trochanter; figs. 45 and 46, from wing, and figs. 47 to 49, from halter. X 1000.
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA
 
 
 
 
481
 
 
 
 
THE ANTENNAL ORGANS
 
 
Several investigators have studied the morphology of the antennal organs in Diptera, but since certain drawings of Hauser ('80), vom Rath ('88), and Nagel ('94) best illustrate the various types of antennal organs, the following discussion will be taken only from these three works.
 
 
The antennae of Diptera are usually short, generally consisting of only a few segments, which bear so-called olfactory pits.
 
 
 
 
 
Hr'
 
 
 
Figs. 50 to 55. Structure of antennal organs of Diptera; figs. 50 to 52, copied from Hauser ('80); figs. 53 and 54, from vom Roth ('88); and fig. 55, from Nagel ('94). Fig. 50, longitudinal section through third or last antennal segment of Cyrtoneura stabulans FIL, showing internal anatomy of segment and the compound olfactory pits (C) in section. X 75. The tip of the segment is not sectioned, thus showing the simple (A) and compound olfactory pits (B) from a superficial view. Fig. 51, section of a simple olfactory pit, and fig. 52, part of a section of a compound olfactory pit; X 750. Fig. 53, section of simple olfactory pit with projecting hair; X 150. Fig. 54, section of compound olfactory pit on palpus; X 100. Fig. 55, 2 olfactory hairs (Hr) on antenna of a mosquito (Culex pipiens cf ) ; X 500.
 
 
 
 
Not all of the segments bear such pits, but the distal or last one is usually well provided with them. Sometimes, however, olfactory pits are never present on any segment, as in the mosquitoes. The olfactory pits are divided into simple and com
 
 
 
482 N. E. McINDOO
 
 
pound ones. From a superficial view, a simple pit looks like a sniall circle (fig. 50, a) with a dot at its center, while a compound pit resembles a large circle (B) which contains radiating lines and two or more dots. Sections through these pits show that a single hair (fig. 51, Br) arises from the bottom of a simple pit and two or more hairs (fig. 52, Hr) from the bottom of a compound pit (fig. 50, C). The mouth and sides of each pit are well protected by pseudohairs (Hr^). A sense cell (SC) lies directly beneath each sense hair and a nerve fiber runs from each sense cell to the nerve (figs. 50 and 52, N). An idea of how well the distal segment is innervated may be had by looking at figure 50.
 
 
Sometimes the hair in a simple pit projects out of the mouth of the pit (fig. 53) , indicating that the primary function of such a hair is that of touch. All types of transitional forms of simple and compound pits have been found, and besides being present on the antennae, the compound pits are sometimes found on the palpi (fig. 54). Mosquitoes do not seem to have olfactory pits; Nagel has found two types of hairs on their antennae, and he calls the short, stout ones (fig. 55, Hr) olfactory organs. A male mosquito has only a few of these hairs, while a female has many. All flies seem to have olfactory pits, but some of them do not have the compound ones, and a few of the latter flies bear only one simple pit on each antennal segment.
 
 
SUMMARY
 
 
The disposition of the olfactory pores on the legs of Diptera is more similar to that of those on the legs of Hymenoptera than to those on the legs of Lepidoptera or Coleoptera, but those on the wings of Diptera are more similar to those on the wings of Lepidoptera than to those on the wings of the other two orders. The disposition of the pores on the halteres is entirely different from that of those on the hind wings of the other orders examined. In Hymenoptera the hind wings bear about one-half as many pores as do the front wings ; in Lepidoptera the hind wings do not bear quite as many pores as do the front wings; while in Diptera the halteres bear almost one-half the total number of pores found. Excluding the abnormal forms, the total number of
 
 
 
 
THE OLFACTORY ORGANS OF DIPTERA 483
 
 
pores found in the four orders examined varies as follows: For Hymenoptera, from 463 to 2608 with 1286 pores as an average; for Lepidoptera, from 514 to 1422 with 850 pores as an average; for Diptera, from 473 to 1550 with 772 as an average; and for Coleoptera, from 273 to 1268 with 724 pores as an average.
 
 
As in Lepidoptera, the olfactory pores of Diptera are domeshaped and their internal anatomy is very similar to that of those in the other three orders, but the sense cells in the halteres are more spherical than usual.
 
 
For description the pores have been divided into four types as follows: The Hicks' type includes all of those on the legs, wings, and a few of those on the bases of the halteres. This type also includes all of those found in the other three orders examined. The other three types are found on the bases of the halteres. The undetermined type really belongs to the Hicks' type, while the basal type is very similar to the Hicks' type; nevertheless, the basal and scalpel types are quite unique and are found only on the halteres. While the basal pores stand in rows resembling the shape of mountain ranges, each row of the scalpel pores may be likened to an inverted urn-shaped ridge whose summit is more or less flat and is beautifully sculptured. Deep depressions lie between the rows in each type and a row of strong, protective pseudohairs stands in each depression. Morphologically, the scalpel type is the most highly developed, but physiologically it is probably little or no better developed than any other type of pore.
 
 
This study indicates that while the hind wings of Diptera have been gradually reduced in size, consequently diminishing their flying ability, their sensory function has been greatly increased.
 
 
Compared with the antennal organs, the olfactory pores are better adapted anatomically to receive olfactory stimuli, because the peripheral ends of their sense fibers come in direct contact with the external air, while those in the antennal organs are covered with hard chitin.
 
 
 
 
484 N. E. McINDOO
 
 
LITERATURE CITED
 
 
Graber, Vitus 1882 Die chordotonalen Sinnesorgane unci das Gehor der
 
 
Insecten. Arch. f. mikr. Anat., Bd. 20, pp. 506-640, 6 pi. Hatjser, Gustav 1880 Physiologische und histologische Untersuchungen ilber
 
 
das Geruchsorgan der Insekten. Zeitsch. f. wiss. Zool., Bd. 34,
 
 
Heft 3, pp. 367-403, 2 pi. Hicks, J. B. 1857 On a new organ in insects. Jour. Linn. Soc. London, Zool.,
 
 
V. l,pp. 136-140, 1 pi.
 
 
1859 Further remarks on the organs found on the bases of the halteres and wings of insects. Trans. Linn. Soc. London, Zool., v. 22, pp. 141-145, 2 pi.
 
 
1860 On certain sensory organs in insects, hitherto undescribed. Ibidem, v. 23, pp. 139-153, 2 pi.
 
 
Lee, A. B. 1885 Les balanciers des dipteres leurs organes sensiferes et leur
 
 
histologic. Rec. Zool. Suisse, T. 2, pp. 363-392, 1 pi. Leydig, Fr.anz 1860 tlber Geruchs- und Gehororgane der Krebs und Insecten.
 
 
Arch. f. Anat. u. Phys., pp. 265-314, 3 pi. McEwEN, R. S. 1918 The reactions to light and to gravity in Drosophila and
 
 
its mutants. Jour. Exp. Zool., v. 25, no. 1, Feb., pp. 49-106. McIxDOO, N. E. 1911 The lyriform organs and tactile hairs of araneads. Proc.
 
 
Phila. Acad. Nat. Sci., v. 63, pp. 375-418, 4 pi.
 
 
1914 a The olfactory sense of the honey bee. Jour. Exp. Zool., v.
 
 
16, no. 3, pp. 265-346, 24 figs.
 
 
1914 b The olfactorj^ sense of Hymenoptera. Proc. Phila. Acad. Nat. Sci., V. 66, pp. 294-341, 3 figs, and 2 pi.
 
 
1915 The olfactory sense of Coleoptera. Biol. Bui., v. 28, no. 6, pp. 407-460, 3 figs, and 2 pi.
 
 
1917 The olfactory organs of Lepidoptera. Jour. Morph., v. 29, no. 1,
 
 
pp. 33-54, 10 figs. Nagel, W. a. 1894 Vergleichend phys. und anat. Untersuchungen iiber den
 
 
Geruchs- und Geschmacksinn und ihre Organe. Bibliotheca Zool.,
 
 
Heft 18, 207 pp. 7 pi. Diptera, pp. 116-117. Prashad, Baini 1916 The halteres of the mosquito and their function. Indian
 
 
Jour. Med. Research, v. 3, no. 3, pp. 503-509, 1 pi. VoM Rath, Otto 1888 tJber die Hautsinnesorgane der Insekten, Zeitsch. f.
 
 
wiss. Zool., Bd. 46, pp. 413-454, 2 pi. Diptera, p. 427. Weinland, Ernest 1890 tJber die Schwinger (Halteren) derDipteren. Zeitsch.
 
 
f. wiss. Zool., Bd. 51, pp. 55-166, 5 pi.
 
 
 
 
AUTHOR S ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, JULT 19
 
 
 
 
REMARKS ON VON MONAKOW'S "DIE LOKALISATION IM GROSSHIRN"!
 
 
F. H. PIKE
 
 
Department of Physiology, Columbia University
 
 
Every now and again a work appears which lays the axe at the root of some of our ancient and honorable scientific assumptions which have survived so long and for years have been so often and so vehemently repeated that they have acquired a certain sacredness and become a part of the dogmatic and uncritical part of our teaching. Verily, the axe hath other uses than those to which it is put by politicians or administrators, and it would seem a pity that a notable work in which certain long-cherished assumptions are put to the test of modern knowledge should escape being brought to public notice. My object is not to give a formal review of the book, but to discourse informally upon some of its unusual features, and particularly those which have to do with the fundamental conceptions of the function of the central nervous system.
 
 
One point in which von Monakow departs from the traditional views is his attitude toward the segmental theory of the nervous system and its necessary attendant hypothesis of shock. Without pausing just here- to give a detailed discussion of his views, we may say that he rejects the segmental theory and limits the effects of shock in so far as they are incompatible with the theory of cerebral localization. It will conduce to the clearness of the discussion to give first a brief account of the older view of the segmental theory of the central nervous system and
 
 
1 Die Lokalisation im Grosshirn und der Abbau der Funktion durch kortikale Herde, von Dr. med. C. von Monakow, Professor der Neurologie und Direktor des hirnanatomischen Institutes sowie der Nerven-Poliklinik aus der Universitat in Zurich. Mit 268 Abbildungen im Text und 2 Tafeln. Wiesbaden. Verlag von J. F. Bergmann, 1914.
 
 
485
 
 
 
 
486 F. H. PIKE
 
 
then take up more in detail the examination of von Monakow's argument against these views and in fa\'or of cerebral localization. , The classical statement of the segmental theory and of the general hypothesis of shock is due largely to Goltz. I made this statement from the point of view of the physiologist rather than that of the anatomist. I should perhaps utter a warning here that the phenomena of shock, as Goltz and others have described it, and as the term is used in this paper, are not to be confused with other phenomena of uncertain nature which have come to be included under the somewhat obscure but widely inclusive term shock as it is used by the surgeon or the clinician. A perusal of the first chapter of von Monakow's work will be sufficient to show the error that may arise from failure to differentiate several different kinds of shock.
 
 
Goltz assumed that all reflexes occurred through the lower levels of the central nervous system and especially through the spinal cord. This view has been restated many times. Perhaps its most concise statement in modern anatomical terms is that by Edinger ('08) :
 
 
Since it is certain that the palaeencephalon persists quite unchanged even after a well developed neencephalon has been added to it, there is no groinid for regarding those activities which we recognize as palaeencephalic in one class of animals as anythmg else or as otherwise localized in higher animals. Furthermore we may regard an entire series of activities as common to all vertebrates and we may then seek to ascertain how other activities are added to these when a new structure is added to the palaeencephalon. All sense impressions and movement combinations belong to the palaeencephalon. It is able to establish simple new relations between the two, but it is not able to form associations, to consti'uct memor}" images out of several components. It is the hearer of all reflexes and instincts.
 
 
This has generally been regarded as a certainty, and despite the fact that he adduces no independent proof, Edinger's italics leave little doubt as to his own views on the subject. But Goltz himself regarded it as an assumption, and no actual proof of its general truth has been forthcoming in the four decades and more since its enunciation. In view of the wide currency
 
 
 
 
die lokalisation im grosshirn" 487
 
 
of the general idea of shock as apphed to the central nervous system it may not be out of place to give here Goltz's statement in his own words, as translated by Loeb ('00) :
 
 
No one will assume, that that piece of the spinal cord which is separated from the brain in so short a time (i.e., a few days or weeks) acquires entirely new powers as a reflex organ; we must assume that these powers were only suppressed or inhibited temporarily by the lesion of the spinal cord.
 
 
Goltz's statement of the segmental theory was that each level or division of the central nervous system had essentially the same functions in all vertebrates (Goltz, '92). The reason why a man or a dog will not recover as completely as a frog or a turtle after loss of the cerebral hemispheres is not because the cerebral hemispheres have any more highly developed motor function in the higher forms, but because the effects of shock are so much more permanent and more severe in the higher forms than in the lower.
 
 
It may be remarked in passing that Magendie (1816), many years before Edinger, had with great clearness stated the mechanism of instincts in neurological terms. An abstract of his views follows :
 
 
We may distinguish, in those attitudes and movements which are intended to express our intellectual and instinctive acts, and which are included under the generic term 'gestes,' between those which are bound up with organization and, as a consequence, are present in all men, in whatever condition, and those which have arisen and reached their perfection in a social state.
 
 
The former are intended to express the most simple condition, the internal sensations as joy, pain, grief and the like, as well as the animal passions, through cries and the voice. One may observe them in the idiot, the savage, the blind from birth, as well as in the civilized man enjoying all moral and physical advantages. These are native or instinctive responses.
 
 
But while Edinger's statement of the relations was probably at variance with the known facts at the time it was made, and certainly is at variance now, the generality of Magendie's expression made it conform, not only to the facts of his time, but also gave it a lease of life which endures to the present day.
 
 
 
 
488 F. H. PIKE
 
 
Von Monakow's views on cerebral localization and on the duration and severity of the effects of shock are at variance with those of Goltz, perhaps raore widely than he realizes. For the substantiation of Goltz's views depends upon either, 1) the direct proof of the activity of the spinal cord in the reflexes in the manner which Goltz supposed it to act in the uninjured animal or, 2) the independent proof that the reflex or other activities of the regions of the nervous system lying below the level of the transection or the injury are merely depressed for days or years, as the case may be, and that no quantitative change occurs in the impulses passing over any given synapse in the lower regions of the nervous system leading to increased activity after the injury, as compared with the amount of activity before the injurj^ occurred. The experimental evidence now available does not substantiate Goltz's conclusions on either of these points.
 
 
Von Monakow recognizes that, if Goltz's view of shock is to be accepted, the idea of cerebral localization must be abandoned, just as Goltz insisted. And if localization is true, one must set some limits to the effects of shock. This he does in his theory of diaschisis, which will be discussed a little later. But if we set anj^ limits to the omnipotence of shock, we raise the question whether shock is a necessary conception in the explanation of the phenomena following injury to any portion of the central nervous system; and, considering shock as a purely depressive effect, whether the limits set may not become vanishingly small. If the limits do become small, the gap between von Monakow's position and Goltz's position must become even wider than it now is.
 
 
It is still necessary to make some assumptions in discussing the organization of the nervous system. Aside from the assumption that the effect of shock is merely temporary and that the cells in the levels below the lesion regain all their former functions in time, von Monakow ('10) makes certain others concerning the organization of the mechanisms of the spinal cord as well as those of higher levels. The account is best given in his own words.
 
 
 
 
"die lokalisation im grosshirn" 489
 
 
From the experiments of Sherrington and others as described, it follows that in the spinal cord of higher mammals and, as my own observations show, apparently even of man, there must be present elements other than the direct receptor and effector cells themselves which retain a stimulus for a longer period than these (i.e., than the direct i-eceptoi's and effectors). Included therein are found nerve cell elements which are excited by individual incoming fibers, facilitated through the summation of stimuli by others and again inhibited by still others. Single nerve cells in the spinal cord apparently return to a condition of rest after a short period of excitation, immediately after the completion of the speciaUzed function assigned to their neurone complex, and again become receptive to new stimuli. Other cells, however, undoubtedly remain in a condition of excitation for a longer period — minutes or more — after the stimulus coming to them has been interrupted. In other words, we find in the spinal cord elements extremely variable in their duration of charge, both positively and negatively (mnestic elements) such as I have long postulated in the bi'ain, with brief, intermediate or long duration of charge (Ladung). There must also be present here well organized groups of neurones which are effective, that is, which can discharge, only b}^ means of a complex summation of stimuli each (action) in a qualitativelj^ different manner and a different duration; and among them are groups which form the connecting links of a chain of acts released in succession, and which remain functional throughout the course of a reflex movement; they carry the 'kinetic melody' as the notes of a chord accompanying the tune."
 
 
Von Monakow's views represent the growth of years. We may take as one starting point the view expressed in 1895 that, in a series of vertebrates, essentially siniilar nervous reactions involve more numerous and more widely scattered groups of cells and fiber tracts in the higher animals than in the lower. The logical development of this idea means abandoning the notion of sharply circumscribed centers particularly in the cerebrum, for various acts, which he does.
 
 
The issue is squarely joined, therefore, with two other opposing camps. There is, on the one hand, the issue between the adherents of the Goltzian view that the effects of shock may persist, undiminished if need be, for months or years, with its consequent negative view of cerebral localization, and the adherents of the view that shock, if present at all, is more or less
 
 
2 1 am indebted to Mrs. C. S. Winkin for assistance in the translation.
 
 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 5
 
 
 
 
490 F. H. PIKE
 
 
transient as one must hold if cerebral localization is to be substantiated. On the other hand, von Monakow opposes those who insist on all the so-called centers in the bulb and cord (and particularly the cerebrum) with which the perverse ingenuity of nvestigators and systematic writers has encumbered the archives and text books of physiology." (Stewart, '00.)
 
 
A complete presentation of the evidence for and against the current ideas of shock and of the omnipotence of the circumscribed centers would require many pages, but some statement is necessary as a basis for a comparison of the various hypotheses and a general estimate of their validity
 
 
As already mentioned, Goltz's view, either in its original form or as restated by Edinger, that reflexes occur through the lower levels of the brain and the spinal cord exclusively, rests upon an assumption. Explicitly or implicitly, Goltz and his school assume that the cells and synapses of the isolated portion of the spinal cord never convey any greater quantity of energy, to use Hughlings Jackson's term, after isolation than they did before. Changes in isolated cells have been mentioned in the Hterature, e.g., Munk's term 'Isolationsanderung,' but those changes have more commonly been supposed to be retrogressive than otherwise. Sherrington's term 'isolation dystrophy,' although applied to a somewhat different condition of affairs, is an instance in point.
 
 
Senator ('98), however, admits that reflexes may be permanently absent in the human subject in cases in which no degeneration of, or damage to, the neurones of the supposed reflex arcs can be shown histologically. Basing his first conclusion, then, upon the fact that some of the reflexes return after a time in the isolated portion of the spinal cord, Goltz as previously indicated, found it necessary to make another assumption, to the effect that the reflexes were only temporarily suppressed or inhibited by the operation of transection of the spinal cord. This temporary failure of the reflexes had been called 'shock' by Marshall Hall, and Goltz spoke of 'Shockwirkung' in this connection. Goltz did not know what shock was, but was inclined to regard it as an 'Inhibitorische Fernwirkung' due to the
 
 
 
 
die lokalisation im grosshirn" 491
 
 
anatomical transection of the cord. And despite the fact that cutting a nerve produces but a relatively small and transient effect as compared with the effects of electrical stimulation, anatomical transection of the spinal cord is commonly said to be a terrific stimulus. Sherrington, however, shows that the effect of anatomical transection can be exerted but once, and concludes that the view of trauma qua trauma as the cause of spinal shock is not really tenable. It has been shown also that shock in the lower levels of the spinal cord may be produced by anaemia of its higher portion and of the brain without interruption of the circulation to the lower portion of the cord (Stewart et al., '06) or by freezing a segment of the spinal cord without excitation of the efferent motor pathway. Sherrington's view that the interruption of certain conduction pathways in the spinal cord favors the production of spinal shock derives much support from these results. The recent w^ork of Ranson ('16) shows that the rupture of certain orally conducting pathways is effective in abolishing responses and that the rupture of the aborally conducting pathways may not be necessary, as Sherrington believed it to be. Ranson's results confirm, in a measure at least, my view that the shock effect is exerted upon the afferent pathway, since the efferent pathway is so obviously open, as judged by all the tests which one may apply.
 
 
The segmental theory of the central nervous system, as Goltz formulated it, does not accord with the facts of organic evolution, inasmuch as it makes no allow^ance for a change in function of the various levels of the system to correspond with the anatomical changes occurring in phylogenetic development. The argument for a shifting of function toward the anterior end of the central nervous axis (Steiner) and the development of cerebral localization is met by the statement on the part of the segmentalists that, if the effects of shock in the higher forms were not so severe, the lower levels of the nervous system of a man would manifest just as complete a recovery after injury to the higher levels as those of a frog. The increasing severity and permanence of the shock effects in higher animals, while freely admitted by Goltz, and even made a supporting point of his
 
 
 
 
492 F. H, PIKE
 
 
hypothesis, are without any explanation on the basis of such an hypothesis. Goltz and his followers conclude that a cell in the lower levels of the central nervous system may never regain all its normal function after the injury to the higher levels.
 
 
Von Monakow departs from the fundamental assumption of the segmental theory — that all levels or segments have essentially the same function in all types of vertebrates — in his statement that more numerous and more widely separated groups of nerve cells and fibers are necessary for the successful execution of essentially similar movements in successively higher types of animals. This statement, as already noted, dates back to 1895. The anatomical and pathological evidence available twenty years and more ago was sufficient to shake his faith in the segmental hypothesis. To some of us it seems that all the additional anatomical, pathological, and experimental evidence which has accumulated since that time points toward cerebral locaUzation as the logical and final development of the processes of evolution in the central nervous system. But, as I have already mentioned, and as I would particularly emphasize now, cerebral localization is an untenable view if all Goltz 's postulates concerning spinal shock are to be granted. The emphasis is the more necessary since this part of Goltz 's argument, which is essentially sound if his premises be granted, has been so frequently neglected or overlooked. Goltz considered the argument against cerebral localization to be just as cogent as his argument for the spinal cord as the great reflex mechanism, as a careful reading of his papers will show. He was much too careful and accurate a thinker to overlook any serious defects in the logic of his argument. Indeed it must be confessed that he was a far clearer and more logical thinker than many who have essayed this field since his day, or than many who have accepted his argument in part while rejecting the remainder of it. The task of these latter authors is more difficult than was Goltz 's, for they must show, not only that one part of his argument is correct, but why the remainder, which is founded on exactly the same assumption as the other part and upon facts of exactly the same nature, is incorrect. I will freely admit
 
 
 
 
die lokalisation im grosshirn" 493
 
 
that intellectual evolutions of this sort are much too difficult for me to follow and, a fortiori, to execute. I cannot do less than to accord to Goltz here, from whom I differ on matters of interpretation, the same tribute he accorded to Le Gallois, from whom he differed on matters of interpretation. I do not question Goltz 's facts any more than he questioned those of Le Gallois. And I should say of him, as he said of Le Gallois, that he was one of the clearest thinkers among the physiologists of his day. But just as the discovery of new facts compelled the revision of Le Gallois' interpretation, so I now beheve that the discovery of new facts has compelled a revision of Goltz's interpretation. The limitation of the effect of shock to a degree which may in some measure be based upon anatomical or functional considerations is necessary. Whereas Goltz supposed that the cells in the regions below the level of injury might never regain all their former degree of activity, but might be permanently depressed or inhibited for the remainder of the life of the animal, von Monakow, while allowing a possible depression of function of the cells below the level of the lesion at the time of its occurrence, supposes that this depression is transient, and that, in time, the isolated cells may regain all their former functions. The minimal deficiencies of function remaining after some weeks or months subsequent to the injury afford a measure of the function of the injured or lost portions, particularly of the upper levels of the nervous system. In no case, so far as T have observed, does von Monakow suppose that the quantity of nervous energy, to use Hughlings Jackson's expression, flowing through any one of the remaining tr:icts is any greater after an animal's recovery from the injury than it was before the injury.
 
 
In his hypothesis of diaschisis, von Monakow comes back to the view that it is the rupture of the aborally conducting, or efferent, paths which is the essential factor in^ shock. The lower lying neurone, after its separation from the higher, or after failure of the impulses which normally come down from the higher, supposedly suffers a temporary depression of function.
 
 
Von Monakow also attacks the idea of a vicarious assumption of the function of the injured portion of the central nervous
 
 
 
 
494 F. H. PIKE
 
 
system by any remaining intact portion, declaring that it is not a useful conception in the explanation of the action of the nervous system normally or of the processes occurring in its recovery from injury.
 
 
If, by vicarious assumption, one means that some other cells and fibers which were never concerned directly or indirectly with the processes carried out by a second group when intact, assume a part of the function of the second group when the latter is injured, vicarious assumption becomes a mischievous as well as a useless hypothesis in the explanation of nervous processes. For, if one group of cells may take over a function with which it has had no previous connection, there is no localization of function in the proper sense of the term. If such be its meaning, the term vicarious assumption of function should be dropped from neurology.
 
 
The idea of compensation in the nervous system for injury to any of its parts should not, however, be disposed of so summarily. In order to show how such a compensation is susceptible of explanation in terms of nerve cells and fiber tracts without violating any of the postulates either of cerebral localization or of localization in the nervous system generally, I will ask leave to introduce here some conclusions to which I have been led from a study of certain processes of compensation for loss of particular afferent channels or central cells and fibers. To state the case intelligibly, it is necessary to give something of the general physiological basis of normal responses.
 
 
I have stated elsewhere my belief that the reactions of an animal generally occur in response to groups of afferent impulses of different kinds rather than to one single kind of afferent impulse. In looking over the field generally. I am more and more impressed with the number of responses in which afferent impulses from more than one source can be shown to participate. I am doubtful whether any single reflex response, particularly a response of the skeletal muscles, can be shown to involve afferent impulses from one source only.
 
 
In making these statements, I am fully aware that in the elicitation of certain reflexes under experimental conditions, one
 
 
 
 
die lokalisation im grosshirn" 495
 
 
nerve trunk only may be stimulated, and it may be urged that the reflex response occurs without the access of any otjier afferent impulses. Stimulation of a particular afferent nerve under constant conditions generally eUcits a particular reflex response. Hermann embodied these facts in his statement of the law of specific response to stimulation. But the reflex response of a skeletal muscle involves other afferent impulses than those arising from stimulation of a given afferent nerve in a given manner, which may be regarded as the particular afferent impulses which elicit the response. Tschiriew showed that even the form of the curve of a single muscle twitch elicited by stimulation of the motor nerve to the nmscle is modified by section of the afferent nerves from the muscle. Afferent impulses from the muscle itself are involved in its reflex response arising from stimulation of any other afferent nerve. And if the muscle is in situ, other, antagonistic, muscles are involved as well as the prime mover. The deportment of the antagonists is controlled by afferent impulses, arising in part in the antagonists themselves, and in part in other regions, such as the joints. The analysis of even the simplest reflex response in an intact animal shows that it is far from simple in the mechanism involved. One should not lose sight of all the other phenomena following the application of the one form of stimulus to a given limited area or location which is said to elicit the reflex. To lose sight of what follows is to get a very imperfect idea of even the simplest reflex response of a skeletal muscle. In general, it is the accessory afferent impulses, if one may so speak of them — the impulses arising from sensory fields other than the limited one to which a given stimulus is applied — which makes the reflex response biologically adequate, to use Edinger's phrase. That a reflex response may occur in the absence of some of the afferent impulses normally entering into its control does not affect the main statement. It is possible that under experimental conditions a reflex could be elicited which would involve afferent impulses from one and only one sensory field. But it is extremely doubtful whether such a condition ever arises in the intact animal. When we consider the liberation of one reflex
 
 
 
 
496 F. H. PIKE
 
 
response by one preceding it, and when we consider also the considerable number of afferent impulses which may be involved in such a reflex response as the maintenance of an attitude of the body or a part of it, or in the maintenance of equilibrium, the actions become bewildering in their complexity.
 
 
The study of the specific reflex response to stimulation of a given afferent nerve and of the modifications of any given response which occur when any particular component of the afferent group is lacking are of importance not only from the point of view of the physiologist, but from the point of view of the clinician as well. One aid in diagnosis which the clinician employs is the study of the modification of typical motor responses which occurs when any particular afferent channel or channels are blocked. Considerably more precision of facts and ideas is necessary before this particular aid attains to its maximum usefulness to the clinician.
 
 
Other writers have also recognized this dependence of the normal response upon afferent impulses from various sources. Upon some such basis, if I get its significance correctly, must the idea of the integrative action, — a summing up of afferent impulses within the central system — of the nervous system be founded. I have expressed elsewhere the belief that the idea of the integrative action of the nervous system is one of the great principles of the physiology of the nervous system. It underlies all the work of Pawloff on conditioned reflexes. And all the work of Pawloff goes to show that it is in the cerebrum that the summing up of the afferent impulses so necessary for the finer sensory discriminations occurs. Instead of being an argument against cerebral localization, as I have once or twice seen intimated, it seems to me that Pawloff 's work is an argument in favor of localization. The description in physiological terms of any response occurring through th» nervous system must include an account of all the afferent impulses which enter into its inception and control, the central mechanism of this integration, and the efferent pathway. The relationships of the various afferent impulses concerned are not always obvious from the anatomical relations. Most of the instances in which
 
 
 
 
die lokalisation im grosshirn" 497
 
 
groups of afferent impulses from different sources are said to be concerned have involved more or less of a subjective element in the demonstration. It is, however, possible to get a purely objective demonstration of the fact that afferent impulses from at least two different sources are involved in postural activity, to use Sherrington's terminology, of the muscles which maintain the position of the head. If one otic labyrinth of a cat is extirpated, there is torsion of the head, the occiput being turned toward the injured side and the nose toward the sound side. If, after an interval varying from one hour to several months, the dorsal roots of the cervical nerves of the opposite side are divided, the torsion of the head disappears (Prince, '16). Subsequent experiments have shown that the processes of compensation are related to a considerable degree to the cerebral hemispheres (Prince, '17). There is a strong presumption, at least, that afferent impulses from divers peripheral sources are normally involved in the control of any motor reaction. All of these impulses of various kinds are necessary for the normal performance of such a motor act. There is also a strong presumption that when one of these afferent channels is blocked by accident or disease, certain of the other channels may, by an increase in the quantity of energy which passes over them, compensate, in part at least, for the loss of the impulses which formerly came in over the damaged pathway. What is commonly called vicarious assumption of function may be a reality in this sense and in this degree. But it is not necessary to postulate the participation in this process of compensation of any system or group of fibers which is not normally concerned in the control of the reactions in some degree. A more detailed account of this phase of the question will be presented in a forthcoming discussion of some unpublished experiments on the otic labyrinth. (See also Wilson and Pike, '12.)
 
 
I wish to say here, however, that the minimal deficiency of function would be an incorrect index of the actual function of such an organ as the otic labyrinth, as the index would be too low. I may remark in passing that Prince's results effectually dispose of the italicized portions of Edinger's remarks on the
 
 
 
 
498 F. H. PIKE
 
 
localization of all reflexes. As the matter appears to me now, I would say that the loss of or injury to any given region of the brain may be compensated for, in part at least, by an increase in the quantity (without any change in the quality), to use a suggestion of Hughlings Jackson's, of the nervous energy passing over the other afferent pathways or through other central stations which are normally involved in the functions of the injured part. Compensatory processes of this general nature should be considered in arriving at an estimate of the normal function of any injured or lost portion of the central nervous system. And if, as I believe has now been definitely shown, these processes do enter into the problem of the interpretation of cerebral function, the minimal deficiency of function observable after a long period of recovery will be too low to serve as an accurate index of the normal function of the injured or lost part. Such a view is not in any way destructive of or antagonistic to von Monakow's argument for cerebral localization. As I see the problem, it strengthens von Monakow's general position inasmuch as it shows that normal cerebral function may be even greater than he imagines.
 
 
The view that more numerous and more widely separated groups of nerve cells and fibers are necessary for essentially the same sort of movement in higher animals than in lower and the view that afferent impulses from different sources are concerned in most of our neuromuscular reactions have a certain bearing on the hypothesis of circumscribed centers each having a definite and particular function. Von Monakow has taken the speech center as a test case and adduces evidence that the cerebral speech mechanism cannot be such a circumscribed center. Space does not permit a consideration of the evidence against such circumscribed centers urged by other physiologists (Leonard Hill).
 
 
There are other systems or mechanisms in which the hypothesis of a definite circumscribed center is no longer satisfactory. One would expect to find such a definite circumscribed region in the lower levels of the nervous system in the portions which have become highly organized, as Hughlings Jackson expresses it,
 
 
 
 
die lokalisation im grosshirn" 499
 
 
and whose responses to excitation occur in a definite regular manner time after time. The group of cells in the medulla oblongata which responds to increase in the concentration of the hydrogen ions in the blood by a respiratory impulse may be taken as a case in point. Probably there is such a definite group of cells from which arise impulses leading to movements of the respiratory muscles, and it is probable also that such impulses do not arise from any other group of cells. The evidence in favor of the normal participation in respiratory movements of accessory respiratory centers in the spinal cord does not appear to me to be conclusive. To this extent and in this sense, the respiratory center is a definite circumscribed center. But the question does not end here. The experimental evidence now at hand on respiratory movements alone is incompatible with the idea of such a circumscribed center as the complete controlling mechanism. Anatomically, the central respiratory mechanism is not very thoroughly known. Experimentally, it is a system of great neurological interest. This interest is heightened for the student of the speech mechanism by the fact that every afferent impulse involved in the control of respiration is involved also in the control of speech. And when we consider that speech involves respiratory movements, most certainly under cortical control, the idea of a circumscribed respiratory center becomes hopelessly inadequate to account for all respiratory movements that are possible in man. A complex mechanism consisting of groups of nerve cells more numerous and more widely separated in man than in the turtle becomes a necessary postulate.
 
 
The argument on shock may be summarized by saying that von Monakow in his theory of diaschisis has granted all that could reasonably be asked for shock, i.e., it is a temporary effect from which the cells recover fully, but never assume any greater function than their normal function in an intact nervous system.
 
 
One may be pardoned, perhaps, for suggesting that, before any hypothesis of shock as a consideration influencing our interpretation of the function of any level of the central nervous system is accepted, we find out just how necessary any such
 
 
 
 
500 F. H. PIKE
 
 
hypothesis is. For any compensatory increase in the activity of the lower neurones must be subtracted from the supposed shock effect, and a corresponding amount must be added to the supposed function of the cerebral cortex, as determined by the criterion of a minimal deficiency of function. As the problem stands at present, there are three unknown quantities: 1) the exact function of the lower neurones, motor, sensory, commissural or association ; 2) the amount of change of a progressive nature rather than retrogressive, which the lower motor neurones undergo after separation from the higher, and, 3) the exact function of the higher neurones. None of the quantities has been measured independently and directly, and the number of equations so far proposed is less than the number of unknown quantities. It seems idle, therefore, to introduce a fourth unknown quantity — the shock effect — or even a fifth, such as vicarious assumption of function, and to ascribe arbitrary limits to it, when the determination of its real value must await either a demonstration of its actual extent and potency or the solution of the equations involving the three other unknowns.
 
 
Certain considerations other than those already adduced may be brought forward in connection with the discussion of von Monakow's views. Diaschisis, or shock, or whatever other name one may apply to the change which occurs in the lower levels of the central nervous system when they are separated from the higher, is a reversible change. I have already referred to Sherrington's statement that, when the shock effect has once been induced in the spinal cord by anatomical transection, a second transection below the first has no further effect. In this case the anatomical separation of one portion of the central nervous system once for all from the remaining portions would preclude any reciprocal action of one part upon the other. No possibility of a reversible reaction dependent upon a connection of the lower levels with the higher exists under such conditions. But when the function of the higher levels of the central nervous system is temporarily abolished, by tying off the arteries to the head, the lower part exhibits at first signs of shock similar to those seen after anatomical transection. There is, however, a
 
 
 
 
die lokalisation im grosshirn" 501
 
 
return of the reflex responses of the structures lying below the anaemic region of the spinal cord within a period of half an hour or an hour. Anatomical transection at this time is not attended by cessation of the reflexes. Just as in Sherrington's experiments, trauma qua trauma is not the necessary antecedent condition for the onset of spinal shock. But if the circulation to the head is restored and the animal is allowed to recover, a more or less normal deportment gradually returns. If anatomical transection of the cord is done on the following day, or even a few hours after re-establishment of the cerebral circulation, signs of shock appear immediately. The changes which occurred in the spinal cord leading to the return of the reflexes while the circulation to the head was interrupted were reversible, since, to all our tests, they did not greatly outlast the period of failure of cerebral and bulbar function.
 
 
There is one other point on which the doctrine of minimal deficiency of function comes into conflict with the conclusions drawn from the results of more acute experiments. Francois Franck and Pitres taught that in mammals tonic movements of the skeletal muscles originated from the lower motor cells (e.g., basal ganglia) and that the clonic movements originated from the higher motor neurones. Epilepsy and epileptiform convulsions (Hughlings Jackson) are of cortical origin. Gowers taught that a spastic paralysis indicated a lesion of the higher motor neurones, while a flaccid paralysis indicated a lesion of the lower motor neurones. Decerebrate rigidity (Sherrington) is due to the activity of lower motor neurones. Horseley reported some experiments from his laboratory in which absinthe was used to induce convulsions in cats. If the cerebral hemispheres were present along with the rest of the central nervous system, absinthe produced clonic convulsions. If the cerebral hemispheres were removed, absinthe produced tonic convulsions. If one cerebral hemisphere was removed and the other left intact, clonic convulsions appeared on the opposite side. So general has the belief in this hypothesis of the origin of tonic and clonic movements become that many have insisted that the pyramidal fibers exert an inhibitory action upon the lower
 
 
 
 
502 F. H. PIKE
 
 
motor neurones. Concerning the truth of this latter statement, I must confess to a deep and enduring skepticism. CompUcations arise in such a scheme. If we follow out the types of movement that are present in various representatives of the vertebrate phylum, we find that even in such forms as the chimaeroid fishes in which higher motor neurones, as we know them in mammals, are lacking, clonic as well as tonic movements are possible. Moreover, in such forms, there is no sustained rigiditj^ of the skeletal muscles: even without the supposed inhibitory action of the pyramidal fibers, the lower motor neurones do not normally develop any activity which results in a prolonged spastic condition of the muscles. If in the higher type of animals the pyramidal fibers exert an inhibitory influence, it seems equally clear that in the course of the evolution of vertebrates a change has occurred in the lower motor neurones, resulting in the development of some activity which must be inhibited. One must therefore admit a change in the function of the lower motor neurones in phylogenetic development if the hypothesis of the tonic inhibitory action of the pyramidal fibers is to be substantiated. Such a change in the function of the lower motor neurones seems improbable. It appears simpler to assume that as evolution has progressed there has been a separation in the types of movement represented by higher and lower motor neurones; and that in the higher animals, when the higher motor neurones are injured or destroyed, there may be a change in the amount of energy passing through — a quantitative but not a qualitative change — in the function of the lower motor neurones. As Dejerine ('14) shows, man is the only form in which a permanent spasticity of the skeletal muscles results from a purely cortical lesion. Goltz's decerebrated dog, in which although decerebration was not complete, no part of the motor area remained, did not exhibit any permanent spasticity. Complete decerebration in a dog is followed, usually within an hour, by marked decerebrate rigidity (Sherrington). The particular nerve cells which it is necessary to rupture in order to produce permanent spasticity have a different anatomical location in man as compared with the dog. Some change in the anatomical
 
 
 
 
die lokalisation im grosshirn" 503
 
 
site of the cells whose renaoval is necessary for the genesis of spasticity by the remaining cells of the central nervous system has occurred in the course of evolution from lower to higher vertebrates. The pyramidal fibers in a dog do not apparently exert the inhibitory effect on the lower motor neurones which they are said to exert in man.
 
 
Spinal shock, while of little direct interest to the present-day internist, has appealed to the clinical neurologists in days past, and from them has come the clinical counterpart of the laboratory expressions. That the necessity for some hypothesis or theory of shock is still felt among clinicians is shown by the fact that Mott ('16) has applied von Monakow's views in the attempt to explain some of the conditions arising in cases of shell shock. It is my opinion that the importance of a conception of the changes occurring in the nervous system as the result of injury will meet with more general recognition as the effects of war conditions are more generally and more critically studied. Two of the earlier attempts of clinicians to explain the effects of injury to or disease of the higher motor neurones are those of Gowers and Hughlings Jackson. Gowers formulated his ideas in terms of inhibition, but, in the opinion of some clinical neurologists, his hypothesis is unsatisfactory. Hughlings Jackson phrased his conceptions in terms of energy. He thought that if one level of the nervous system was damaged by disease about the same quantity of energy as passed through the whole central system before the injury passed through the remaining levels after the injury. Although he does not expressly say so, Jackson's view, particularly in the form in which it was expressed by Horsley ('07), postulates a quantitative change in the number or intensity of impulses going through the remaining nervous pathways. I can hardly see how the change in the amount of energy in the remaining levels of the central nervous system which he imagines to occur after the shutting out of one level can occur without such a quantitative change as has been shown to occur in some levels of the central nervous system. To all intents and purposes, the idea of a quantitative change in function must have been present in Jackson's mind. I do not
 
 
 
 
504 F. H. PIKE
 
 
remember, either, that he used the term vicarious assumption of function. It is true that Jackson was not an experimentaUst, but his powers of observation and of deducing from his facts a generahzation which would hold them all together were extraordinarv. In the matter of cerebral localization, he anticipated by several years the experimental work of Frits ch and Hitzig. The idea of a change of energy in the remaining levels of the central nervous system should, from its authorship, command at least a careful scrutiny. But aside from some of the fruitful suggestions of Luciani, I have seen little or no use made of the hypothesis by experimentalists, despite the fact that such a hypothesis might be given the rank of a fundamental assumption. I am strongly of the opinion at present that we have experimental proof that a given conduction pathway may carry a greater quantity of nervous energy after injury to another path way associated with it in the control of a given response than it carries under the usual conditions.'
 
 
' Prof. W. M. Bayliss, who has read the manuscript, has asked me just what the earlier statement of Jackson about the change in the quantity of nerve energy passing over a given pathway might mean in terms of the recent work of Lucas and Adrian on the nerve impulse. One may take as an example of such a change the crossing over of efferent impulses from the respiratory center at the phrenic nuclei. (Porter, Journal of Physiology, 1894-5, 17, p. 455). The reader must consult the original paper for the full description of the phenomena, as it is too long to give here in detail. When the spinal cord is hemisected above the level of origin of the phrenic nerve, we will say on the right side, the movements of the half of the diaphragm on that side cease. If the phrenic nerve of the opposite (uninjured or left) side is divided, the movements of the right half of the diaphragm begin again. The impulses which were passing down the left side of the cord now cross to the right side. As I see it, there is a change in the quantity of nervous energy passing over the commissural fibers and synapses from the left phrenic nucleus to the right. It is possible, even probable, that the increasing asphyxial condition which comes on after section of the left phrenic nerve leads to the excitation of more cells in the bulbar respiratory center and to the sending out of impulses over more efferent fibers than before. It is not necessary to postulate any increase in the intensity of the impulses coming over any one fiber. In view of Stirling's demonstration that the synapses have the power of summation of impulses, and Sherrington's experiments, as well as observations by G. N. Stewart and myself, pointing to the same conclusion, I think it probable that the principal change occurs in the passability of the synapses. In the compensations occurring after loss of the otic labyrinth, it does not seem possible that either more fibers are excited in any of the afferent systems entering
 
 
 
 
"die lokalisation im grosshirn" 505
 
 
One reason for the neglect of Jackson's hypothesis may be that Jackson's conception is distinctly that of a physiologist, while clinicians generally have tried to interpret the nervous system without much reference to purely physiological data. The physiologist has generally given too little consideration to well established clinical data, and has often exercised too little critical discrimination with regard to widely current beliefs which were not necessarily in accordance with the facts. I find Jackson's views in general better suited to constructive work than Goltz's.
 
 
The odds in favor of any hypothesis of shock and against cerebral localization could scarcely be greater than von Monakow has granted. He has understated rather than overstated his case. To my mind, therefore, one of the fundamental questions in the physiology of the nervous system, and in fact the question that underlies practically all of our interpretation of the effects of lesions of the central nervous system today, is whether or not a nerve cell, or group of cells, perhaps forming a potential reflex arc, in any way increases quantitatively, after injury to a system connected wdth it, the work which it has been doing while all its connections are intact. Unless the possibility of such a quantitative change can be excluded, the whole hypothesis of shock must be modified. And if such a quantitative change can be shown in such an isolated (speaking relatively, of course) group of nerve cells, even von Monakow's conclusions must be modified in favor of a stricter view of cerebral localization than the one he now holds.
 
 
If von Monakow is right in his conclusions from anatomical data, and, as I have insisted elswhere, they derive great support from the experimental data, Edinger's dictum becomes definitely obsolete, and takes with it all the obscurity and vagueness of the shock hypothesis, as well as, let us hope, some of its acrimony.
 
 
into the process of compensation or that impulses passing over these fibers are any more intense than before. There may be an increased sensitivity of some of the receptors, but it seems probable that the main thing is the change of resistance at the synapses.
 
 
On the basis of the all or none law, it is difficult to see how such a severe effect as has sometimes been supposed to result from transection of the spinal cord is possible.
 
 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 5
 
 
 
 
506 F. H. PIKE
 
 
But, if the rigid conceptions of the segmental system are to be substantiated and shock in all its pristine vigor is to remain with us, then must it be conceded that von Monakow has been pursuing a mirage and that the inferences from the great amount of fact collected in his volume are largely untrue. This I am loath to admit, since my own interpretations of experimental findings would be swept away with it. I may repeat that it is necessary to choose between the hypothesis of spinal shock and the segmental theory, on the one hand, and the theory of cerebral localization, on the other. The adherent of the theory of cerebral localization need not be unduly troubled by misgivings as to the security of his position until it has been shown beyond mere assumption that the things supposed to occur in shock actually do occur. So far as the experimental evidence goes at present, it is against Goltz's position rather than in favor of it. Whatever objections I may urge against von Monakow's position are to be regarded as constructive rather than destructive. Neither of us doubts the transient effect of shock nor the general truth of cerebral localization. I believe that the available evidence justifies a stricter view, a more rigid locaUzation than the one he has propounded in his volume.
 
 
The doctrine of cerebral localization must be regarded as established, and the hypothesis of shock as Goltz formulated it must be discarded. Not only has there been no direct proof of the hypothesis of shock, but there is experimental proof of the main tenets of the theory of cerebral localization. There must be a corresponding revision of many of the chapters in our texts of physiology as they stand today.
 
 
The establishment of the theory of cerebral localization will bring us a step nearer to the realization of the prophetic vision of Magendie ('l6b), which has been obscured for so many decades by the mass of detail accumulated by anatomists and experimentalists ahke, both of whom have so far failed to accept the interpretation of the great French experimentaUst.
 
 
One means by the term brain (cerveau), the organ which fills the cavity of the cranium and that of the spinal canal. To facilitate the study, the anatomists have divided it into three parts, the ceiveau
 
 
 
 
"die lokalisation im grosshirn" 507
 
 
(brain) properly speaking, the cerebellum, ^nd the spinal cord. This division is purely scholastic. In reality the three parts form one and the same organ.
 
 
It is only when we regard the cerebrum as the great sensory and motor mechanism to which all the other parts contribute and from which they receive that we can rid ourselves of the idea — eminently fallacious, as I view it — of independent sensory or motor activities of other portions of the nervous system and begin to see all parts of the system acting as one system.
 
 
We are hearing much of the clearness of French thought in relation to scientific subjects at the present time. It is well that we are beginning to accord it the somewhat tardy recognition which it so nobly deserves. I am minded to emphasize the value of clear thinking in science and particularly in physiology, by a quotation from another source. In the German edition of Luciani ('07), but unfortunately omitted from the English edition, there is a fine sentence concerning another very prevalent fallacy — the view that the otic labyrinth has its main functional pathway through the cerebellum — but which is equally applicable to the popular status of shock to-day.
 
 
One cannot deny that the clearness and consistency of the book by ... . leave something more to be desired, and its following among many chnicians and surgeons would be difficult for me to explain if I did not remember that great is the number of uncritical people among whom words of uncertain meaning have more weight than positive facts and clear, well considered explanations.
 
 
The plausibility of the words of uncertain meaning may be greater than that of the other type of exposition. How else may one account for the amazing vogue of fakirs and quacks? It may be remarked in passing that von Monakow inclines to the view that there is a cortical station for laybyrinthine fibers in the cerebrum.
 
 
More recently, Luciani ('16), has warned against the confusion in thought which inevitably follows when one fails to recognize the essential unity of action of the central nervous system, but clings instead to the idea of separate, independent, and sharply localized centers in various divisions of the central
 
 
 
 
508 F. H. PIKE
 
 
nervous system. As I have indicated elsewhere, some conception of a quantitative change in the amount of energy passing over a given nerve pathway after injury to another may have been present in Luciani's mind years ago.
 
 
Von Monakow's work will take its rank along with other classical monographs on the nervous system — Francois-Franck's Lecons sur les Fonctions Motrices du Cerveau," Luciani's Cervelletto" and Soury's Le systeme nerveux centrale." It is to be hoped also that the various illuminating addresses and lectures which were published during the j^ears when the larger volume was in preparation will be continued long after its publication.
 
 
The objection sometimes urged against works in the German language that American work does not receive proper consideration can scarcely be urged against von Monakow's volume. American anatomists, psychologists, clinical neurologists, and surgeons are mentioned in the index of authors. The small number of American physiologists whose work is cited may perhaps be taken as index of the lack of interest in this phase of physiology which has been manifested by American workers.
 
 
 
 
die lokalisation im grosshirn" 509
 
 
BIBLIOGRAPHY
 
 
Dejerine, J. 1914 Semiologie des Affections du Systeme Nerveux. Paris, p.
 
 
Edinger, L. 1908 The relations of comparative anatomy to comparative psychology. Jour. Comp. Neur., 18, p. 444.
 
 
GoLTZ, F. 1892 Der Hund ohne Grosshirn. Archiv fiir die Gesammte Physiologic, 51, p. 614.
 
 
HoRSLEY 1907 Dr. Hughlings Jackson's views of the function of the cerebellum, as illustrated by recent research. Brit. Med. Jour., April, p. 803
 
 
LoEB, J. 1900 Comparative physiology of the brain. New York and London, pp. 273-4.
 
 
LuciANi, L. 1907 Physiologic des Menschen. Jena. Bd 3, p. 488.
 
 
1916 La questione del moto e del commino in ordinc alia dottrina del cervellctto. Archivio di Fisiologia 14. pp. 147-156.
 
 
Magendie, F. 1816a Precis Elelmentaire de Physiologic. Paris; T. 1, pp.
 
 
302, 303.
 
 
b Ibid, p. 162 MoNAKOW, C. von 1895 Experimentelle und pathologisch-antomischc Unter suchungen iiber die Haubenregion, den Sehhiigel und die Rcgio sub thalamica, etc. Archiv fiir Psychiatric, 27, pp. 1, 386.
 
 
1910 Aufbau und Lokalisation der Bewegungcn bcim Menschen.
 
 
Leipzig, p. 12. MoTT, F. W. 1916 The effects of high explosives upon the central nervous
 
 
system. Lancet, 1, pp. 331, 441, 545. *
 
 
Pike, F. H. 1909 The genera' phenomena of spinal shock. Amer. Jour.
 
 
Physiol. 24, pp. 139-142. Prince, A. L. 1916 The position of the head after experimental removal of
 
 
the otic labyrinth. Pro. Soc. Exper. Biol, and Med., 13, p. 156.
 
 
1917 On the compensation of the ocular and equilibrium disturbances which follow unilateral removal of the otic labyrinth Ibid, 14, p. 133, and unpublished results. See also Aronovitch, B., and Pike, F. H.,
 
 
1918 The factors influencing the attitude of the head in animals with injury to one otic labyrinth. Science, N. S.. 47, p. 519.
 
 
Ranson, S. W. 1916 New evidence in favor of a chief vaso-constrictor center
 
 
in the brain. Amer. Jour. Physiol., 42, p. 1. Senator, H. 1898 Zwei Falle von Querschnittscrkrankung des Halsmarks.
 
 
Zcitschrift fiir klinische Medizin, 35, p. 18. Sherrington, C. S. 1906 The integrative action of the nervous system New
 
 
York, p. 246. Stewart, G. N. 1900 Manual of physiology, 4th ed. London and Philadelphia,
 
 
p. 717. Stewart, G. N., et al. 1906 The resuscitation of the central nervous system of
 
 
mammals. Jour. Exper. Med., 8, p. 289. Wilson, J. G., and Pike, F. H. 1912 The effects of stimulation and extirpation of the labyrinth of the ear and their relation to the motor system.
 
 
Part 1. Experimental. Philosophical Trans. Royal Soc, London,
 
 
Series B., Vol. 203, p. 127.
 
 
 
 
AUTHOR S ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, AUGUST 7
 
 
 
 
WEIGHTS OF VARIOUS PARTS OF THE BRAIN IN
 
 
NORMAL AND UNDERFED ALBINO RATS
 
 
AT DIFFERENT AGES
 
 
C. A. STEWART Institute of Anatomy, University of Minnesota, Minneapolis
 
 
ONE FIGURE AND THREE TABLES
 
 
CONTENTS
 
 
Material and methods 512
 
 
Brain 5I5
 
 
Cerebrum 519
 
 
Brain stem 521
 
 
Cerebellum 522
 
 
Olfactory bulbs 523
 
 
Discussion 524
 
 
Summary 526
 
 
Bibliography 527
 
 
In connection with an earlier study of the changes in the relative weights of the various organs in underfed albino rats (Stewart, '18 b), the brain was observed to manifest a remarkable tendency toward continued growth in very young animals, even when increase in body weight was prevented. The work has been extended in the present investigation to a more detailed consideration of the growth of separate parts of the brain in severely stunted rats. In addition, a considerable number of observations was made on the weights of different parts of the brain in normal rats at various ages. This phase of the w^ork, however, was discontinued when I learned that Prof. H. H. Donaldson, of The Wistar Institute of Anatomy, Philadelphia, had undertaken the latter problem upon an extensive scale. Fortunately, we had each selected the same brain subdivisions for consideration, so that direct comparison of our results is possible. Dr. Donaldson has kindly furnished me with a record of his data for
 
 
511
 
 
 
 
512 C. A. STEWAKT
 
 
stock albino rats (presented in part in a Harvey Lecture, December, 1916) which in general are in agreement with my own observations upon normal animals. Only my own data are presented in this paper, however. This opportunity is taken to acknowledge my indebtedness to Prof. C. M. Jackson for valuable advice given during the course of the present experiments.
 
 
MATERIAL AND METHODS
 
 
In the present investigation the brains of 64 normal (31 males, 33 females, table 1), and of 29 test rats (19 males, 10 females, table 2) were used. Among the 64 normal rats are included 22 individuals which also served as the direct controls for the test rats. The rats used were all Albinos (Mus norvegicus albinus) from the colony in the Institute of Anatomy here.
 
 
The number and sex of the normal animals killed at the selected periods between birth and adult age are shown in table 1. Of the direct controls (table 2), 12 rats (8 cf , 4 9 ) were killed at birth (average weight 4.7 to 5 grams), 9 rats (5 d^, 4 9 ) at approximately 10 grams, and one male at 12 grams body weight.
 
 
The test rats were repeatedly starved by isolation from the mother for various periods as described elsewhere (Stewart, '18b). In this manner 15 individuals (9 cT', 6 9) were held approximately at birth weight for periods ranging from 5 to 18 days; and 13 rats (9 c/', 4 9 ) were permitted to increase shghtly in weight reaching approximately 10 grams at 3 weeks of age. In addition one male was weaned when 21 days old, body weight 10.5 grams, and was placed upon a limited diet of whole wheat (Graham) bread and whole milk. At 56 days of age this individual weighed only 12 grams.
 
 
It will be noted that the average final body weight is practically the same for the control and the test rats of each group (table 2) . In comparing the data for the normal and the starved individuals, the slight differences existing in body weight have been disregarded. This seems justified since the error involved is small and cannot obscure the changes produced by the experimental conditions. Strictly speaking, however, a slight correction should be made as previously noted (Stewart, '18 b).
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS
 
 
 
 
513
 
 
 
 
TABLE 1
 
 
Number and sex of rats, body weight and length, and weight of the brain with the percentage weights of its various subdivisions in normal rats at various ages
 
 
 
 
NUMBER, SEX, AND AGE OF RATS
 
 
 
 
2 cf
 
 
4 cf ,
 
 
 
 
4 9 , Newborn... . 2 days
 
 
4 days
 
 
5 days
 
 
6 days
 
 
19.8 days
 
 
19.9 days
 
 
19, 10 days
 
 
11 days
 
 
12 days
 
 
14 days
 
 
39, 21.3 days
 
 
28 days
 
 
35 days
 
 
29, 42.6 days
 
 
2 9, 49.6 days....
 
 
63 days
 
 
4 9, 70 days
 
 
1 9, 114 days.. ..
 
 
1 9, 127 days.. . .
 
 
2 9 , 143 days. . . .
 
 
/ o^ 357 days \ 9 454 days
 
 
 
 
GROSS
 
 
BODY
 
 
WEIGHT
 
 
 
BODY
 
 
LENGTH
 
 
 
BRAIN WEIGHT
 
 
 
PER CENT OF BRAIN CEREBRUM
 
 
 
PER CENT
 
 
OP
 
 
BRAIN
 
 
STEM
 
 
 
PER CENT OF BRAIN CEREBELLUM
 
 
 
grams
 
 
 
mm.
 
 
 
grams
 
 
 
 
 
 
 
 
 
4.86
 
 
 
48.61
 
 
 
0.2086
 
 
 
64.4
 
 
 
29.3
 
 
 
3.65
 
 
 
5.40
 
 
 
50.0
 
 
 
0.2640
 
 
 
62.4
 
 
 
30.3
 
 
 
4.28
 
 
 
6.00
 
 
 
5
 
 
 
0.3545
 
 
 
67.6
 
 
 
25.6
 
 
 
5.64
 
 
 
8.50
 
 
 
58.0
 
 
 
0.4400
 
 
 
68.6
 
 
 
22.5
 
 
 
5.43
 
 
 
10.00
 
 
 
62.0
 
 
 
0.5135
 
 
 
69.4
 
 
 
22.4
 
 
 
5.36
 
 
 
9.80
 
 
 
62.0
 
 
 
0.6259
 
 
 
71.7
 
 
 
18.8
 
 
 
6.55
 
 
 
10.5
 
 
 
66.52
 
 
 
0.6969
 
 
 
71.4
 
 
 
19.1
 
 
 
6.32
 
 
 
10.35
 
 
 
65.0
 
 
 
0.6699
 
 
 
71.2
 
 
 
18.8
 
 
 
7.33
 
 
 
9.50
 
 
 
62.0
 
 
 
0.7451
 
 
 
70.1
 
 
 
18.7
 
 
 
8.06
 
 
 
11.00
 
 
 
5
 
 
 
0.6838
 
 
 
70,9
 
 
 
19.3
 
 
 
7.01
 
 
 
15.00
 
 
 
5
 
 
 
0.9994
 
 
 
69.2
 
 
 
17.6
 
 
 
10.2
 
 
 
23.2
 
 
 
86.03
 
 
 
1.2800
 
 
 
67.1
 
 
 
16.2
 
 
 
12.8
 
 
 
28.0
 
 
 
97.0
 
 
 
1.2087
 
 
 
65.1
 
 
 
16.6
 
 
 
13.5
 
 
 
33.0
 
 
 
105.0
 
 
 
1.3500
 
 
 
65.0
 
 
 
16.9
 
 
 
13.7
 
 
 
53.2
 
 
 
126.3
 
 
 
1.4389
 
 
 
64.3
 
 
 
17.3
 
 
 
13.2
 
 
 
41.5
 
 
 
115.6
 
 
 
1.2026
 
 
 
63.1
 
 
 
18.3
 
 
 
14.3
 
 
 
73.5
 
 
 
141.0
 
 
 
1.5856
 
 
 
63.7
 
 
 
17.8
 
 
 
14.2
 
 
 
96.1
 
 
 
149.0*
 
 
 
1.5962
 
 
 
63.6
 
 
 
18.0
 
 
 
13.9
 
 
 
142.5
 
 
 
176.0
 
 
 
1.6084
 
 
 
64.4
 
 
 
18.8
 
 
 
13.9
 
 
 
131.1
 
 
 
169.5
 
 
 
1.6839
 
 
 
61.4
 
 
 
19.4
 
 
 
14.1
 
 
 
164.7
 
 
 
182.5
 
 
 
1.7015
 
 
 
62.1
 
 
 
20.3
 
 
 
13.8
 
 
 
c^257.0
 
 
 
c^212.0
 
 
 
 
 
 
 
 
 
 
 
9 213.0
 
 
 
9197.0
 
 
 
1.8100
 
 
 
60.8
 
 
 
21.8
 
 
 
14.0
 
 
 
 
2.51
 
 
3.12
 
 
1.31
 
 
3.47
 
 
2.75
 
 
2.93
 
 
3.15
 
 
2.65
 
 
3.14
 
 
2.79
 
 
3.04
 
 
3.69
 
 
4.47
 
 
33
 
 
83
 
 
15
 
 
62
 
 
58
 
 
 
 
4
 
 
4
 
 
4
 
 
4
 
 
4
 
 
2.90
 
 
5.01
 
 
3.81
 
 
2.92
 
 
 
 
1 Average of 10 individuals. - Average of 2 individuals. 3 Average of 5 individuals. ■• Average of 6 individuals. 5 Not recorded.
 
 
 
 
The rats were killed either by chloroform or (in a few cases) by bleeding. The body (nose-anus) and tail lengths were immediately measured in the usual manner. The head was subsequently severed at a point immediately behind the foramen magnum. The brain was then carefully removed (care being exercised to preserve the cerebellar paraflocculi) and weighed in a closed container on balances accurate to 0.1 mgm.
 
 
 
 
514 C. A. STEWART
 
 
The brain was next placed upon a moist plate of glass and its various parts dissected as follows. The olfactory bulbs were removed by a vertical incision at the point where they pass beneath the frontal lobes of the cerebrum. The cerebellum was then removed by severing its various crura or peduncles. Finally the cerebrum was separated from the brain stem by an incision immediately anterior to the superior colliculi passing through the anterior part of the crura cerebri. The cerebrum thus included the telencephalon (except olfactory lobes) and diencephalon, and the brain stem included the midbrain, pons, and medulla oblongata. The four brain subdivisions thus obtained were placed in a moist chamber and later carefully weighed in a closed container.
 
 
In all cases there is some difference between the total weight of the separate parts and the initial brain weight, due no doubt, either to evaporation from, or to fluid adhering to, the subdivisions weighed. Fortunately, however, the error is generally small and insignificant, especially as compared with the changes in weight that have occurred in the test rats. Based on the assumption that the error is probably distributed more or less proportionately among the various portions of the brain weighed, an attempt was made to correct the existing error n computing the percentage for each subdivision, by using the total weight of the separate parts rather than the original brain weight.
 
 
The observations in table 1 upon normal rats less than three weeks of age are grouped only in instances where there were two or more individuals of the same age. Later, when the brain growth is less rapid, the data have been averaged, grouping individuals differing a few (usually three or four) days in age. In the case of the eight adult rats only is there any considerable range in ages. Since the sexual difference in brain weight in anim^als of corresponding weight is comparatively small (Donaldson, '08, '09), the observations for males and females of each group have been combined. This is also justified by the relatively small number of observations, since the individual variations would obscure any existing difference according to sex.
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 515
 
 
In table 2 the data for the control groups and for the test rats are likewise grouped, only the averages being given. The original individual observations will be filed at The Wistar Institute of Anatomy and Biology (Philadelphia), where they may be consulted by those interested.
 
 
A preliminary report of the present investigation appeared in the Proceedings of the American Association of Anatomists, Minneapolis Meeting, December, 1917 (Stewart, '18a).
 
 
BRAIN
 
 
The weight of the entire brain (table 2) is considerably higher in the various groups of test rats than in the corresponding younger controls of the same body weight. In the fifteen individuals (9 cf, 6 9) held at birth weight for various periods there is an increase from an average (sexes combined) of 0.2086 gram in the newborn controls to 0.4468 gram in the test rats, an increase of about 114 per cent. An inspection of the individual data in table 2 shows that the increase is greater in those rats held at maintenance for longer periods.
 
 
As may be observed in table 2, the body length also increases, although the body weight is held constant. The brain weight is also much greater in the stunted animals than in normal rats of the same body length, although the difference is not so great as when those of the same body weight are compared.
 
 
In the test rats weighing about 10 grams at 3 weeks the relative increase is less, amounting to approximately 33 per cent; while at 56 days with body w^eight at 12 grams the excess of brain weight in the test rats is about 30 per cent. In an earlier report (Stewart, '18 b) the brain in rats underfed from birth and weighing 10 grams at 3 weeks of age was found to exceed that in normal rats of corresponding body weight by about 60 per cent, which is considerably more than the excess obtained for a comparable group in the present series. In general, however, the results agree in showing a stronger growth tendency of the brain in the younger and smaller rats.
 
 
The increase in brain weight in spite of underfeeding with nearly stationary body weight is probably best shown in figure 1
 
 
 
 
 
 
B
 
 
 
 
B
 
 
 
 
 
 
C C
 
 
Fig. 1 A and A', dorsal and ventral view, respectivelj', of brain of normal newborn rat. Body weight, 5.4 grams. Brain weight, 0.238 gram. X 3.
 
 
B and B', dorsal and ventral view, respectively, of brain of rat kept at birth weight by underfeeding for 20 days. Body weight, 5 grams. Brain weight, 0.506 gram. X 3.
 
 
(Conlintiadoti of explanation of fi^] ares on page opposite.)
 
 
516
 
 
 
 
PARTS or BRAIN IN NORMAL AND UNDERFED RATS
 
 
 
 
517
 
 
 
 
TABLE 2
 
 
 
 
Number, sex, weight, and length, with weights of the brain and its various parts in normal and underfed rats at different ages
 
 
 
 
NUMBER, SEX, AND AGE OF RATS
 
 
 
GROSS
 
 
BODY
 
 
WEIGHT
 
 
 
BODY LENGTH
 
 
 
BRAIN
 
 
 
CEREBRUM
 
 
 
STEM
 
 
 
CEREBELLUM
 
 
 
OLFACTORY BULBS
 
 
 
8 cf, Control, newborn.... 1 Test d, 5 days
 
 
 
grams
 
 
4.97
 
 
4.7
 
 
5.5
 
 
4.6
 
 
4.8
 
 
5.8
 
 
5.0
 
 
5.5
 
 
5.5
 
 
5.8
 
 
 
mm,.
 
 
49.11 56.0 56.0 55.0 53.0 57.0 57.0 59.0 57.0 60.0
 
 
 
grams
 
 
0.2106 0.3653 0.3872 0.3743 0.4711 0.5348 0.4790 0.5404 0.4920 0.4571
 
 
 
0.1375 0.2481 0.2724 0.2563 0.3368 0.3742 0.3413 0.3845 0.3464 0.3247
 
 
 
0.0622 0.1085 0.0940 0.1027 0.1014 0.1143 0.1134 0.1334 0.1062 0.1053
 
 
 
0.0079 0.0213 0.0232 0.0213 0.0307 0.0356 0.0335 0.0346 0.0334 0.0291
 
 
 
0.0055
 
 
0.0151
 
 
 
1 Test cf , 6 days
 
 
 
0.0118
 
 
 
1 Test cf , 7 days
 
 
 
0.0150
 
 
 
1 Test d, 12 days
 
 
1 Test d, 12 days
 
 
1 Test d, 12 days
 
 
1 Test d, 13 days
 
 
1 Test cf , 14 days
 
 
1 Test d, 14 days
 
 
 
0.0154 0.0246 0.0192 0.0242 0.0220 0.0180
 
 
 
Average, 10.6 days
 
 
 
5.24
 
 
 
56.7
 
 
 
0.4557
 
 
 
0,3205
 
 
 
0.1088
 
 
 
0.0292
 
 
 
0.0184
 
 
 
4 9 , Newborn
 
 
 
4.65
 
 
4.9
 
 
4.0
 
 
4.8
 
 
5.0
 
 
5.0
 
 
5.1
 
 
 
47.52 54.0 52.0 55.0 54.0 56,0 54.0
 
 
 
0.2046 0.3603 0.3728 0.4434 0.5079 0.4019 0.5212
 
 
 
0.1323 0.2549 0.2564 0.3139 0.3444 0.2892 0.3732
 
 
 
0.0611 0.0999 0.1033 0.1018 0.1068 0.0872 0.1180
 
 
 
0.0074 0.0205 0.0212 0.0262 0.0328 0.0256 0.0415
 
 
 
0.0048
 
 
 
1 Test 9, 5 days
 
 
 
0.0149
 
 
 
1 Test 9, 11 days
 
 
1 Test 9 , 12 days
 
 
 
0.0154 0.0180
 
 
 
1 Test 9, 12 days
 
 
1 Test 9, 13 days
 
 
1 Test 9, 18 days
 
 
 
0.0204 0.0142 0.0216
 
 
 
Average, 12 days
 
 
 
4.8
 
 
 
54.1
 
 
 
0.4346
 
 
 
0.3053
 
 
 
0.1028
 
 
 
0.0280
 
 
 
0.0174
 
 
 
5 Control cf , 9 days
 
 
9 Test d, 22 days
 
 
4 Control 9 , 9.5 days
 
 
4 Test 9, 22 days
 
 
1 Control d, 9 days
 
 
1 Test d, 56 days
 
 
 
10.2 10.4 9.6 9.6 12.0 12.0
 
 
 
63.0
 
 
67.8 63.3 65.9 69.0 77.0
 
 
 
0.6309 0.8837 0.6845 0.8444 0.7324 0.9544
 
 
 
0.4589 0.6169 0.4830 0.5894 0.5304 0.6312
 
 
 
0.1280 0.1578 0.1282 0.1477 0.1340 0.1856 1
 
 
 
0.0396 0.0956 0.0497 0.0896 0.0556 0.1210
 
 
 
0.0181 0.0265 0.0212 0.0229 0.0240 0.0410
 
 
 
 
Average of 7 individuals. 2 Average of 3 individuals.
 
 
 
 
On comparison with the brain of the newborn rat (A and A'), it is evident that during underfeeding (maintenance) not only the brain as a whole, but also the olfactory bulbs and tracts, cerebral hemispheres, colliculi, cerebellum and flocculi, tuber cinereum, pons, and medulla continue to grow in young rats in spite of practically no change in body weight for 20 days. Comparison with the normal brain at 20 days (C and C), however, shows that the growth of the various parts of the brain mentioned above, while considerable, nevertheless has been greatly retarded.
 
 
C and C, dorsal and ventral view, respectively, of brain of normal rat at 20 days of age. Body weight, 17.5 grams. Brain weight, 1.047 grams. X 3.
 
 
 
 
518
 
 
 
 
C. A. STEWART
 
 
 
 
{a, a', newborn control; b, h' , test rat). As compared with the control of the same body weight, not only the various subdivisions weighed, but also the olfactory tracts, tuber cinereum, corpora quadrigemina, and especially the para flocculi are evidently much larger in the starved rat.
 
 
Although considerable brain growth thus occurs during maintenance of constant body weight in young rats, nevertheless it occurs at a greatly retarded rate in comparison with the normal growth during the corresponding period of time. This is so well shown in figure 1 (h, h' and c, c') that a lengthy discussion is unnecessary.
 
 
TABLE 3
 
 
Comparison of relative intensity of growth of various parts of the brain in normal
 
 
and test rats
 
 
 
 
Cerebellum .... Olfactory bulbs
 
 
Cerebrum
 
 
Brain stem
 
 
 
 
PERCENTAGE BT WHICH THE WEIGHT OF THE VARIOUS PARTS OF THE BRAIN
 
 
 
 
At 11 days exceeds that at birth
 
 
 
 
Normal
 
 
 
 
696 351 293 130
 
 
 
 
Test
 
 
 
 
272 240 131
 
 
72
 
 
 
 
At 3 weeks exceeds that in normal lO-gram rats
 
 
 
 
Normal
 
 
 
 
274
 
 
144
 
 
85
 
 
63
 
 
 
 
Test
 
 
 
 
113 30 29 20
 
 
 
 
In older rats held at maintenance for various periods, investigators in general have noted practically no change in the brain weight. Thus Hatai ('08) found the brain weight in stunted rats to be practically identical with that for normal younger rats of the same body weight. In a large series of rats studied by Donaldson ('11), after maintenance from 30 to 51 days of age, the brain exceeded the calculated initial weight by only 3.6 per cent. Jackson ('15 a) and Stewart ('16) conclude that there is practically no change in the weight of the brain in rats held at maintenance for various periods starting at 3 weeks of age. Holt ('17) noted a slight increase in brain weight in undersized rats fed upon an unsuitable diet of whole corn after the period of weaning.
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 519
 
 
Aron ('11) publishes data showing in a few instances the brain weight in greatly stunted dogs practically equal to that in normal heavier dogs of the same age. However, no observations were made concerning the initial brain weight at the beginning of the experiment and the extent of the brain growth which apparently occurred during the underfeeding is therefore uncertain.
 
 
It is interesting to note that Variot and Lassabliere ('09) found the growth of the brain in underfed infants to be retarded less than the growth in body weight, the brain thus increasing at the expense of other tissues of the body. This observation agrees with my own results for young albino rats.
 
 
During severe starvation a slight decrease in the weight of the brain was noted by Bechterew ('95) in puppies and kittens, and by Hatai ('04) in young rats. Acute and chronic inanition in adult rats causes but little if any loss in absolute brain weight (Jackson, '15 b). A very complete summary of the literature bearing upon the effect of inanition upon the brain is given by Jackson ('15 b).
 
 
CEREBRUM
 
 
If the percentages are calculated from the combined weight of the separate brain parts, it appears that the cerebrmn (table 1) (telencephalon and diencephalon, excluding olfactory bulbs) during normal growth increases from an average of slightly more than 64 per cent of the entire brain at birth (sexes combined) to a relative maximum of approximately 71 per cent during the early part of the second week. Thereafter, although increasing in absolute weight, the cerebrum forms a progressively smaller proportion of the brain, decreasing to an average of approximately 67 per cent (sexes combined) at three weeks, and to about 61 per cent at one year and later. My results agree fairly well with those of Hatai ('15) for adult individuals of approximately similar body length, with those of Sugita ('17) for the rat during the first 150 days, and also with the unpublished data of Donaldson (personal communication). Slight differences appear which are presumably due partly to experimental error and partly to normal variability in the size of the brain segments.
 
 
 
 
520 C. A. STEWART
 
 
In the stunted rats kept at birth weight for various periods, and also in those weighing approximately 10 and 12 grams at three and eight weeks, respectively, the weight of the cerebrum (table 2) considerably exceeds that of the normal younger controls of corresponding body weight. For the first group (sexes combined) there is an increase from an average of 0.1358 gram in the controls to 0.3144 gram in the test rats, an increase of more than 131 per cent. In the test rats at three weeks (22 days) the increase in the cerebrum is relatively less, amounting to approximately 29 per cent, and at eight weeks it has decreased to about 19 per cent.
 
 
As to relative proportions, the percentage weight of the cerebrum is slightly higher in the test rats kept at birth weight various periods than in the controls, the apparent increase being from an average of approximately 64 per cent of the combined weight of the separate parts in the latter to 67 per cent in the stunted individuals. The range in the test rats is from about 63 per cent to 69 per cent, increasing in general with the length of the experiment. If we now compare the corresponding change in relative proportion of the cerebrum during normal growth, it is evident that with the increase in brain weight from birth there is normally an increase in the percentage that the cerebrum forms of the entire brain, similar and practically equal to that noted in the brain of equal size in the stunted rats.
 
 
In the test rats weighing about 10 grams at three weeks, however, there is apparently a slight decrease (71 to 69 per cent) in the relative size of the cerebrum as compared with the controls of the same body weight. Likewise during normal growth there is a similar decrease in the percentage weight of the cerebrum while the brain weight is increasing from about 0.6500 gram to 0.8700 gram. At eight weeks of age the cerebrum in the test rats, though absolutely larger, is relatively smaller than in the control. This change likewise is probably associated with the usual tendency toward declining relative size of the cerebrum in normal brains of corresponding weight, although the difference in this case is greater than would be expected from the apparent change during nonnal growth.
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 521
 
 
In general, therefore, the data indicate that during the persistent growth of the brain, in very young rats stunted by underfeeding, the cerebrum (telencephalon and diencephalon) maintains the same relative size as in the normal brain of corresponding weight.
 
 
BRAIN STEM
 
 
The percentage weights (calculated from the combined weights of separate brain subdivisions) for the brain stem (including: midbrain, pons, and medulla oblongata) show a relative decrease from an average of about 29 per cent of the normal brain at birth to about 16 per cent at three weeks. Subsequently the growth of the brain stem is more rapid than that of the brain as a whole, resulting in a gradual increase in relative weight to an average of about 22 per cent in the adult rats. The normal initial decrease and subsequent increase in the relative size of the brain stem is in agreement with the observations by Sugita ('17) and Donaldson (unpublished data). As compared with adult animals of corresponding body length, my results correspond fairly well with those obtained by Hatai ('15).
 
 
In the stunted rats held at birth weight for various periods, and also in the other groups of test animals, the weight of the brain stem (table 2) in all cases considerably exceeds that in the younger controls of the same body weight. In the first group there is an increase from an average of 0.0618 gram (sexes combined) for the controls to 0.1064 gram in the test rats, an increase of approximately 72 per cent. In the test rats at three and eight weeks of age, the increase in brain stem weight amounts to about 20 and 39 per cent, respectively.
 
 
As to relative proportions, the brain stem in the rats held at birth weight apparently decreases from about 29 per cent (in the controls) to about 22 per cent of the brain weight. In the test rats at 22 days the brain stem weight has further decreased to about 18 per cent, as compared with 19 per cent in the controls of similar body weight. In the test rat at 56 days, however, the brain stem has slightly increased to 19 per cent (18 per cent in the control).
 
 
THE JOURNAL OF COMPARATIVE NBUROLOQT, VOL. 29, NO. 5
 
 
 
 
522 C. A. STEWART
 
 
In these cases, however, the relative size of the brain >tem in the brain of the stunted rats corresponds approximately to that in normal brains of the same weight. The only exception is that of the single test rat in which the brain stem should be relatively slightly smaller than in the control, according to the change found in the normal brains of corresponding weights. The difference is slight, however, and may be obscured in this case by individual variation or experimental error.
 
 
On the whole, therefore, it appears that during the persistent growth of the brain, in very young rats stunted by underfeeding, the brain stem (midbrain, pons, and medulla) maintains approximately the same relative size as in the normal brain of corresponding weight.
 
 
CEREBELLUM
 
 
Calculations from the data obtained show that during postnatal growth the cerebellum (table 1) apparently increases rapidly from an average of about 3.7 per cent of the total weight of the separate parts of the brain at birth (sexes combined) to about 14 per cent at seven weeks of age, and maintains approximately this relative weight in the adult albino rat. In general these results agree fairly well with those obtained by Hatai ('15) (for adult rats of body length similar to that of my adult controls), by Sugita ('17) (from birth to 150 days of age), and by Donaldson (unpublished data).
 
 
In the rats underfed for various periods the cerebellum (table 2) shows a remarkable growth. In the individuals held at birth weight the cerebellum has increased from an average of 0.0077 •gram in the controls (sexes combined), to 0.0287 gram, an increase of over 272 per cent. At three and eight weeks of age the increase in the test rats is approximately 113 and 118 per cent, respectively, as compared with the younger controls of the same body weight.
 
 
As to relative proportions, the cerebellum is in all cases found relatively much larger in the brain of the test rats, in comparison with that in control rats of the same body weight. If the percentage of the brain weight formed by the cerebellum in the test
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 523
 
 
rats (table 2) is compared with that in normal brains (table 1) of the same weight, however, the agreement is surprisingly close. It is therefore apparent that during the persistent growth of the brain in underfed young rats the cerebellum, like the segments previously considered, maintains approximately the same relative size as in the normal brain of corresponding weight.
 
 
OLFACTORY BULBS
 
 
Calculations from my data (table 1) indicate that the olfactory bulbs, although rather variable, in general increase from an approximate average (sexes combined) of 2.5 per cent of the total weight of the separate parts of the brain at birth, to about 3.7 per cent at three weeks, and probably reach a relative maximum of about 4.8 per cent at six or seven weeks of age. Subsequently their relative weight decreases in the majority of cases, reaching about 2.9 per cent in the adult. Attention should be called to the fact that the data indicate not only a relative decrease, but even an absolute loss in the weight of the olfactory bulbs in the older rats. In general my results agree with those obtained by Hatai ('15), Sugita ('17), Holt ('17), and Donaldson (unpublished data) for normal albino rats, the existing differences probably being due partly to normal variability and partly to experimental error.
 
 
In the stunted rats the olfactory bulbs greatly exceed those in the younger controls of the same weight (table 2). For the group held at birth weight there is an increase of nearly 240 per cent. For the other test animals at three and eight weeks of age the increase is less marked, amounting to 30 and 71 per cent, respectively.
 
 
The percentage that the olfactory bulbs form of the entire brain weight, especially in the case of the individuals kept at birth weight for various periods, averages higher than that for the newborn controls. According to my data, accompanying an increase in brain weight from approximately 0.2100 gram to 0.4500 gram there is normally a considerable increase in the relative weight of the olfactory bulbs, although apparently not so great as in the stunted rats with brains of corresponding weight.
 
 
 
 
524 C. A. STEWART
 
 
Thus the olfactory bulbs appear relatively larger in the stunted rats than in normal rats of the same brain weight.
 
 
For the group fasting three weeks the relative increase is slight and inconstant. In the normal rats with corresponding brain weight (0.6309 to 0.8837 gram) the relative weight of the olfactory bulbs is likewise nearly stationary, though somewhat variable. This is in agreement with Holt ('17), who found the relative proportions of the olfactory bulbs to remain practically unchanged in rats undersized after four and eight weeks of feeding upon an unsuitable diet of whole corn.
 
 
The data for my rat underfed from birth to eight weeks indicate an apparent increase in the relative weight of the olfactory bulbs, which is in accordance with the general tendency toward an increase in the relative size of olfactory bulbs in normal rats with brains of corresponding weight. Miss Holt noted a tendency for the bulbs to increase in relative weight during prolonged defective feeding in rats weighing about 50 grams.
 
 
On the whole it therefore appears that during the persistent growth of the brain in underfed young rats the olfactory bulbs tend to maintain a relative size similar to that in the normal brain of corresponding weight. In the youngest and smallest group, however, they apparently become relatively hypertrophied and appear relatively larger than in normal animals with the same brain weight.
 
 
DISCUSSION
 
 
Quite uniformly the results of experiments have shown that the brain demonstrates a marked ability to grow when increase in body weight is prevented by underfeeding only in very young animals and at a time when the normal growth of the brain is very pronounced. There is, therefore, apparently a definite relation between the increase in size accomplished during starvation and the normal growth power possessed by the organ at the time when underfeeding is commenced That this dependency upon the intensity of the growth impulse applies also to the various parts of the brain is evident upon comparison of the relative rapidity of growth of the various parts of the brain in young rats.
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 525
 
 
As is shown in table 3, in both the normal and test rats, the cerebellum manifests the strongest growth power, the olfactorybulbs, cerebrum, and brain stem following in the order mentioned. The perfect agreement in this respect between the control and test individuals can hardly be considered a mere coincidence, but more probably is the expression of inherent normal tendencies.
 
 
Furthermore, it has been pointed out that with the growth of the brain in the stunted rats, the various portions of the brain undergo practically the same changes in relative size as found in normal animals of the same brain weight. The olfactory bulbs which show an overgrowth (in the younger group) apparently form the only notable exception to this rule. In general, therefore, it appears that normal growth tendencies foreshadow the character and the amount of the changes that accompany growth of the brain during underfeeding. In other words, the growth of the brain in the stunted rats appears normal, so far as the changes in the size of the constituent parts is concerned.
 
 
The tendency for the different brain subdivisions to maintain largely the normal proportions during starvation is in marked contrast to the change in the relative weights produced among various organs of the body as to result of underfeeding. Jackson ('15, p. 152) also noted that in some cases (e.g., liver, alimentary canal) there is a certain degree of parallelism between the normal growth tendency and the behavior of organ weight in young rats when the body weight is held constant. Furthermore, the greatest number of organs showing growth during maintenance (constant body weight) occurs in very young rats during the normal period of most rapid growth (Stewart, '18). The above-mentioned principle therefore applies not only to the brain and its various subdivisions, but also to many other organs. However, there are certain exceptions to this rule, as pointed out by Jackson.
 
 
It is interesting to note that the marked growth of the brain in rats stunted by underfeeding occurs only at a period when the normal increase in size is still due partly to cell multiplication, especially in the cerebellum (Allen, '12). This is a phase of the inanition problem worthy of further investigation.
 
 
 
 
526 C. A. STEWART
 
 
SUMMARY
 
 
1 . The weights of various parts of the brain were studied in 64 normal rats at various ages, and also in 29 test animals, of which 15 individuals were held at birth weight by underfeeding for periods ranging from 5 to 18 days of age, 13 rats were permitted to increase slightly in weight reaching approximately 10 grams at 3 weeks, and one male weighed 12 grams at 56 days of age.
 
 
2. According to the data available, the cerebrum (excluding olfactory bulbs) increases from a normal average of slightly more than 64 per cent of the entire brain at birth, to a maximum of about 71 per cent during the early part of the second week, but subsequently forms a progressively smaller proportion of the brain, decreasing to an average of about 61 per cent in the adult.
 
 
The brain stem (including midbrain, pons, and medulla oblongata) decreases from a normal average slightly exceeding 29 per cent of the brain at birth to about 16 per cent at 3 weeks, but later increases reaching a relative weight of about 22 per cent in adult animals.
 
 
The cerebellum increases rapidly from an apparent average of 3.7 per cent of the entire brain at birth to about 14 per cent at 7 weeks of age, and thereafter.
 
 
The olfactory bulbs, while variable, in general increase from ail average of about 2.5 per cent at birth to 3.7 per cent at 3 weeks, and probably reach a relative maximum of slightly more than 4.5 per cent at 6 or 7 weeks of age. Subsequently there is a gradual decrease in relative weight to about 2.9 per cent in the adult rat. The data indicate not only a relative decrease, but even an absolute loss in the weight of the olfactory bulbs in the older rats.
 
 
3. For the stunted rats the weight of the brain as a whole in the individuals held at birth weight for various periods averaged 1 14 per cent higher than that in the controls, whereas the excess in test rats weighing 10 grams at 3 weeks and 12 grams at 8 weeks of age was 33 and 30 per cent, respectively.
 
 
As shown in figure 1, the increase is shared not only by the various brain parts dissected and weighed, but also by the olfactory tracts, tuber cinereum, colliculi, and the paraflocculi.
 
 
 
 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 527
 
 
Of the various parts of the brain, the weights of the cerebellum, olfactory bulbs, cerebrum, and brain stem exceed those for the control rats of corresponding weight in the order mentioned, the greatest change occurring in the individuals kept at birth weight for various periods. In this group of individuals the different parts of the brain in the order above listed show an increase of 272, 240, 131, and 72 per cent, respectively.
 
 
In the persistent growth of the brain in the young rats stunted by underfeeding, the various parts of the brain in general preserve approximately the same relative weight as in normal individuals of the same brain weight. The olfactory bulbs apparently form an exception to this rule, as they become abnormally large in the younger group of stunted rats. This apparent hypertrophy may be due, however, to experimental error.
 
 
BIBLIOGRAPHY
 
 
Allen, E. 1912 The cessation of mitosis in the central nervous system of the albino rat. Jour. Comp. Neur., vol. 22, no. 6, pp. 547-568.
 
 
Aron, Hans 1911 Nutrition and growth. Philippine Jour. Science, vol. 6, no. 1, pp. 1-51.
 
 
Donaldson, H. H. 1908 A comparison of the albino rat with man in respect to the growth of the brain and of the spinal cord. Jour. Comp. Neur., vol. 18, no. 4, pp. 345-392.
 
 
1909 On the relation of the body length to the body weight and to the weight of the brain and of the spinal cord in the albino rat (Mus norvegicus var. albus). Jour. Comp. Neur., vol. 19, no. 2, pp. 155-167.
 
 
Hatai, S. 1908 Preliminary note on the size and condition of the central nervous system in albino rats experimentally stunted. Jour. Comp. Neur., vol. 18, no. 2, pp. 151-155.
 
 
1915 The growth of the body and organs in albino rats fed with a lipoid-free ration. Anat. Rec, vol. 9, no. 1, pp. 1-20.
 
 
Holt, C. M. 1917 Studies on the olfactory bulbs of the albino rat. In two parts: I. Effect of a defective diet and of exercise. II. Number of cells in bulb. Jour. Comp. Neur., vol. 27, no. 2, pp. 201-259.
 
 
Jackson, C. M. 1915 Changes in the relative weights of various parts, systems, and organs of young albino rats held at constant body weight by underfeeding for various periods. Jour. Exp. Zool., vol. 19, No. 2, pp. 99-156. 1915 e Effect of acute and chronic inanition upon the relative weights of the various organs and systems of adult albino rats. Am. Jour. Anat., vol. 18, no. 1. Also abstracted in Proc. Amer. Assn. Anatomists. Anat. Rec, vol. 9, no. 1, p. 90.
 
 
 
 
528 C. A. STEWART
 
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