Talk:Book - Contributions to Embryology Carnegie Institution No.44

INTRODUCTION.

The pathological condition of internal hydrocephalus is intimately connected with abnormalities of the production or absorption of cerebro-spinal fluid. The first explanation of this condition — an increased elaboration of the fluid by the choroid plexuses — remains a hjqDothetical possibility. Obstruction to the normal pathways of drainage of the fluid has been many times demonstrated anatomically, so that now this idea of the origin of the disease may be considered to rest on a firm basis. It is with the experimental production of that type of hydrocephalus, due to obstruction to the flow of the cerebro-spinal fluid through its normal channels, that this paper will deal.

To insure a more complete understanding of the anatomical problems under- lying internal hydrocephalus, a short review of the essential morphological and physiological features of the pathwaj^s of the cerebro-spinal fluid will be given. The conception that the greater part of the cerebro-spinal fluid is produced by the choroid plexuses of the cerebral \entricles is no longer strongly controverted; when first advanced, it had only the glandular histology of the plexus to support it (Faivre, 1853; Luschka, 1855), but much later a combination of pharmacological, histologi- cal, and pathological observations indicated beyond question the essential role of these plexuses in the elaboration of this body-fluid. From a summary of this evi- dence and from personal study IMott (1910) suggested the term "choroid gland" for these vascular structures. More recently embryological studies related the first extraventricular flow of the fluid to the initial tufting of the plexuses (Weed, 1916 a and h; 1917). Pathologically, the production of an internal hydrocephalus by tumors occluding the ventricular passages has been recognized for years as affording evidence of an intraventricular source of the fluid.

From the choroid plexuses the fluid is poured into the cerebral ventricles which are lined by ependj^mal cells of ectodermal origin. The fluid from the lateral ventricles escai^es through the foramina of IMunro into the third ventricle, thence through the aqueduct of Sylvius into the fourth. Additions to the fluid are made by the choroid plexuses of the third and fourth ventricles. From the fourth ventricle this fluid passes into the mesodermal subarachnoid spaces through the foramina of IMagendie and of Luschka, if these be actual openings, or at least through permeable membranes if the patency of the foramina be questioned.

The cerebro-spinal fluid leaving the ventricular system, is distributed from the cisterna cerebello-meduUaris, which it first reaches on leaving the fourth ventricle. In the comparatively large channels about the base of the brain the flow is rapid and great; down the cord the dispersion is also fairly efficient, but over the convexities of the cerebral hemispheres a very slow and less eflEicient distribution occurs. Everj'where this extraventricular course is through the meshes of the subarachnoid spaces— a complicated, interrupted fluid-channel, completely clothed by low or flat mesothelial cells. In the cisternal regions, and to a lesser extent about the ujjper spinal cord, the mesh of this fluid channel is rather large, but over the hemi- spheres it becomes quite small. The pial reflection of the mesothelial cells lining the subarachnoid space is broken by the openings of the perivascular spaces (Robin) ; into these cuff's the mesodermal cells continue for a short distance. By way of these perivascular spaces a small but rather important fluid, representing probably the elimination of the brain tissue, is added to the subarachnoid cerebro-spinal fluid.

It seems quite well estabUshed that the cerebro-spinal fluid is returned directly into the blood stream. This escape of fluid is wholly from the subarachnoid space; all observers are agreed that the intraventricular absorption is minimal. The most important hj'potheses regarding the mode of absorption of the fluid are those which assume the Pacchionian vilh as the pathways into the dural sinuses (Key and Retzius, 1876) ; that the fluid reaches the cerebral capillaries by way of the peri- vascular sheaths (Mott, 1910); or that a direct absorption into the capillaries of the subarachnoid space occurs (Dandy and Blackfan, 1913, 1914). More recently evidence that the arachnoid villi (normal projections of arachnoidea into the dural sinuses) are the essential structures in the pathway of escape, has been presented (Weed, 1914, a, b, c). The direction of flow (toward subarachnoid space) in the perivascular spaces argues against Mott's idea of drainage, while the absence of capillaries in the arachnoid renders the hypothesis of Dandy and Blackfan unten- able. The strongest evidence, both anatomical and physiological, favors the idea of a major absorption from the cranial portion of the subarachnoid space.

With this conception of the pathway of the cerebro-sjjinal fluid, it becomes evident that the obstruction to outflow of fluid may be either intraventricular or extraventricular. Pathologically, the differentiation of hydrocephalus into two classes with reference to the point of obstruction has repeatedly been made. In the one, the block to outflow occurs usually at the points of constriction of the ventricular system, as at the foramina of Munro, witliin the aqueduct of Sylvius, or (in rarer cases) within the fourth ventricle. In the second variety of cases the obstruction to flow of the fluid occurs within the subarachnoid space. The mechan- ism of this intrameningeal block is not well understood, except in the cases of obvious fllling of the cisterna cerebello-meduUaris with fibrinous exudate, occasioning a macroscopic closure of the exit.

The occurrence of a typical internal hydrocephalus due to block witliin the narrow portions of the ventricular systems seems of easy explanation. With con- tinued elaboration of cerebro-spinal fluid by the choroid plexuses, and practically no intraventricular absorption, it seems inevitable that dilatation of the ventricles should take place. Such enlargement reaches its fullest expression in the lateral ventricles with compression and thinning of the cerebral cortex. With the increased pressure of the fluid there is ultimately brought al)out a ])ahincc between the production of fluid by the choroid i)lexuses and the minimal intraventricular absorption, plus other potential agencies of escape.

But when consideration is given to the enlargement of the lateral ventricles from obstruction to flow within the meninges, a plausible explanation is more difficult. The mere mechanical explanation does not fairlj^ meet the question as to why the meningeal block does not cause compression of the cerebral cortex, dila- tation of the subarachnoid spaces, and a typical external hydrocephalus. In one variety of this type (obstruction at the foramina of the fourth ventricle) the mechan- ical explanation holds. But actually, a diffuse block to the outflow of cerebro- spinal fluid within the meninges results almost inevitably in the later production of an internal hydrocephalus.

CHnically, a differentiation between the two types of internal hydrocephalus may be made. In children Gushing (1908) found that the cerebral ventricles of one kind of internal hydrocephalus (due to block in the meninges) could be drained by lumbar puncture, while in the other (due to block in the ventricular system) the cerebral ventricles could be emptied only from the ventricular needle. Similarly, Dandy and Blackfan (1913, 1914) recovered by lumbar needle phenolsulpho- nephthalein injected into the cerebral ventricle in the "communicating" type, while the subarachnoid absorption was markedly retarded. In the obstructive type these writers showed a negligible absorption from the cerebral ventricles, but an unim- paired absorption from the subarachnoid space. In these cases the dye injected into the dilated ventricles did not appear as normally in the lumbar fluid.

Experimentally, the obstructive type of hydrocephalus alone seems to have been produced. Dandy and Blackfan (1913, 1914) were able to cause a typical internal hj^drocephalus in dogs by two methods, the first of which gave the patho- logical picture of an intraventricular block. Pledgets of cotton were introduced from the occipital region through the fourth ventricle into the aqueduct of Sylvius. Such a foreign obstruction caused signs of cerebral pressure (lethargy, vomiting) and a rather acute dilatation of the ventricles was produced. In a somewhat different way the same enlargement of the ventricles was accompUshed b}' Ugation of the vein of Galen, but this occurred in only one of the ten animals used. In the other nine animals the higher Ugation apparently permitted sufficient collateral circulation. Dandy and Blackfan used young dogs 2 to 6 months of age; at this time in the dog the cranial sutures are strongly united, so that no enlargement of the head occurred. The time allowed for the dilatation of the ventricles varied from three to eight weeks after the operation. At the end of this period a fair degree of hydrocephalus was present.

At about the same time Thomas (1914) published the results of his experiments on the production of an internal hydrocephalus by the intraventricular injection of aleuronat in starch. This protein caused a marked inflammatory reaction, blocking finally the ventricular pathway at one or other of the narrow parts. Dogs were used throughout for the observations. Thomas found Httle enlargement of the ventricles present in the first week, but in the chronic stage of the inflammatory process incited bj^ the protein, an internal hydrocephalus developed, wdth s>Tnp- toms of increased intracranial pressure. The dilatation of the lateral ventricles occurred slowly and reached its maximum in about two months. Subsequent intra-

ventricular injection of India ink demonstrated that the obstruction to flow of the cerebro-spinal fluid occurred, in the different animals, either at the foramen of Munro, in the aqueduct of Sylvius, or most frequently, at the foramen of Magendie. It must be emphasized that in many cases the ventricular dilatation was markedly asymmetrical (the greater enlargement being on the side of the injection) and that the ventricular wall was often irregularly eroded. The intraventricular accumu- lation of fluid was associated with a steril(> inflammatory process.

An attempt to produce an internal hj'drocephalus in kittens was made by Burr and ]\IcCarthy (1900). These authors described a case of internal hydrocephalus in man with a macroscopically boggy ependjona. Microscopically, the sections showed proliferation of ejjendyma and neuroglia, interstitial infiltration of the choroid plexuses, and some perivascular invasion with inflammatory cells. As the nature of the lesion in this case suggested to these workers a toxic irritant, intra- ventricular injections of sterilized urine, glycerine extract of the adrenals, tuber- culin, hydrochloric and carbohc acid were made in kittens. No dilatation of the cerebral ventricles occurred in these animals, though similar ependymal and glial changes were reproduced.

Flexner (1907) recorded the occasional production of an internal hydrocephalus in monkej'S following lumbar subarachnoid injection of meningococci. Of one subacute case of meningitis he wrote :

"A striking feature of the sections is derived from the width of the ventricles. As a rule, these appear as slits in the sections; in this case they are wide cavities. Usually, the ependynial epithehum is regular and relatively high; in this case, it is often depressed or flattened, and a considerable flattening of the choroid plexus, toward the wall of the ven- tricle, is noticeable. A considerable degree of sub-epithelLal cellular proliferation has taken place in the walls of the lateral and fourth ventricles. Leucocytes are moderately abundant in the ventricles."

METHOD OF INVESTIGATION.

The method of investigation in this study developed out of the idea that it would be possible to produce an internal hydrocephalus in animals if a sterile meningitis of appropriate type and distribution could be caused. This assumed that the meningeal variety of obstruction to flow of the cerebro-spinal fluid was an experimental possibility and the agencies were selected with this end in view.

In a i^revious report (Weed, 1917) notation was made of the fact that, following the subarachnoid injection of inert carbon particles, evidence of phagocytosis on the part f)f the cells lining the subarachnoid space could be made out. By increasing the quantity of this inert substance it was hojied that a more extensive reaction of inflammatory cells and of the arachnoidea could be brought about. Quite similarly it was i)roposed to make subarachnoid or intraventricular injections of other insol- uble particles. It was desired i)riinarily to reproduce a hydrocei)lialus in a very young animal, so that a typical enlargement of the head, com])arable to the fairly common condition in children, might be i)roduced. To accomplish this, it was felt that the experimental procedure must be necessarily simple and uninvolved.

Fortunately almost the first technical procedure resulted in the production of a typical internal hydrocephalus. A litter of kittens two weeks old was obtained;

a 5 per cent suspension of lampblack in Ringer's solution was injected into the lateral ventricle of one animal, and the others of the litter were used for injection of other materials or for control. The head of the kitten receiving the intraventricular lampblack enlarged ; the fontanelles widened markedly and a typical clinical picture of the desired condition resulted.

Subsequently the technical procedure was modified in many ways. E.xperi- ments demonstrated that a somewhat more pronounced pathological change, with less disturbance of the kittens' activities, could be produced by subarachnoid injec- tion of the lampblack through a needle in the occipito-atlantoid ligament. This latter method alone was employed in the experiments on adult cats. In the earlier cases two intraventricular injections of lampblack were sometimes given with an interval of several days between; later it was found that this double injection was useless, provided the concentration of the carbon in the initial injection were great enough. Customarily, in both cats and kittens, as much cerebro-spinal fluid as possible v,-as allowed to escape from the occipito-atlantoid or ventricular needle; injections of 1 c.c. (in kittens) to 10 c.c. (in adults) of a 5 to 10 per cent suspension of lampblack in Ringer's solution were made through the needle after the release of fluid. The lampblack originally injected was found to be more efficacious than any other sample tested; it is sold under the trade name of "Germantown Black" and is manufactured by the L. Martin Co., New York City. Other lampblacks produce a similar condition of hydrocephalus, but not as rapidly or as invariably as does this Germantown Black. Whether tliis difference in reaction is due to difference in size of granulation or to some other "binder" in the carbon is not known.

The intraventricular or subarachnoid introduction of these carbon granules was controlled by similar injections of equal amounts of other insoluble granules in suspension. Because of its wide employment as an injection-medium, cinnabar (red mercuric sulphide) was selected as the routine control granule. None of the particular insoluble substance used for this purpose gave rise to an internal hydro- cephalus, but it does not seem improbable that other insoluble granules may be found to produce such a pathological change.

A point of considerable practical importance in the care of kittens subjected to experimental procedures concerns the return of the animals to the mother with- out apparent change. In these experiments the hair was not shaved in the area of puncture and the kittens were returned to the mother only when fully recovered from the anesthesia. With these simple precautions it was possible to inject kittens one day of age and to have the mother subsequently take care of them as well as the others in the Utter. In general, kittens up to four weeks of age were subjected to the experimental injections; these gave the greatest enlargement of the cranium and remained fairly well for the greatest lengths of time.

At the end of varying periods the animals (both kittens and adult cats) were sacrificed and injected with 10 per cent formaUn through the aorta, as were those d^dng from the experimental procedure or from bronchial infection (a common difficulty in such animals). After hardening for a suitable period further macro- scopic studies were made and the heads were sectioned.

432 THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. THE REACTIONS OF THE EXPERIMENTAL ANIMALS.

Age is apparently a determining factor in the reactions of an animal after the intraventricular or subarachnoid injection of lamj^black. Probably more important than the actual age of the animal is the associated degree of ossification of the skull; if the vmion between the bony plates is marked and firm, the increase in intracranial tension does not result in any enlargement of the bony skull. This enlargement of the head, met with in kittens after the subarachnoid or intraven- tricular injection of suspensions of lampblack, seems to be compensatory in nature and allows much more cerebral function than is possible in an adult animal with a rigid skull. The experimental findings in the immature and in the adult animals will in consequence be detailed under separate headings.

KITTENS.

In all, 35 kittens were given subarachnoid or intraventricular injections of suspensions of lampblack. These kittens were from 18 fitters and at the time of experimentation were normal, healthy animals. The age at the time of experi- mentation ranged from 24 hours to 42 days. The younger animals were all being taken care of by the mothers, whereas the older in the series were being fed as adults.

As the technical procedure of injection was very simple, practically none of the animals died acutely as the result of the experiment. Of the 35 kittens used, 8 died (or were sacrificed because of poor physical condition) within the first 8 days; 8 survived for more than 4 and less than 10 days; and the remainder (19) lived for over 10 days. The longest period of survival after the experimental injec- tion was 47 days. The cases considered to be most successful and showing most pronounced enlargement of the head were those which lived more than 14 days after the experimental injection. The number of the animals in the series surviving for several days is really surprisingly large, and the proportion of early deaths, con- sidering the age of the animal at the time of the experiment, was very low.

No real or essential difference between the reaction of the kittens receiving subarachnoid or intraventricular injections could be made out. Possibly, those receiving the lampblack into the subarachnoid space showed enlargement of the head somewhat more rapidly and remained in better physical condition for a longer period. By both routes, however, the production of an internal hydrocephalus seems equally certain, provided a suitable dose (best, about 1.0 c.c. of a 10 per cent suspension) of lampblack be given. The release of cerebro-spinal fluid by needle thr(»ugh th(! occipito-atlantoid ligament is much more certain than is ventricular puncture through the fibrous fontanelle or through the thin bone of a young kitten. Pathologically, there is practically no difference in the hydrocephalus resulting from either procedure; the amount of carbon particles found in the cerebral ven- tricles is, however, much smaller in the animals receiving the occipito-atlantoid injection. In these experiments the most extreme cases of internal hydrocephalus have been those produced by such subarachnoid injection. Of 35 animals, 19 were given intraventricular and 16 subarachnoid injections.

On recovery from the ether, these experimental kittens with subarachnoid or intraventricular injection can hardly be told from the normal control animal in the litter. If abnormal at all, they tend to be somewhat less active in crawling about and seem cautious in movements, particularly in regard to the head. The next morning the experimental animal usually did not cUffer from the control, though a slight carefulness and slowness in reaction might be present (noted in 5 out of 16 cases). On the second morning, in the more pronounced cases of obstruction, an enlargement of the head has been made out; this is usually demonstrated by the formation, again, of suture lines preA-iousl.v closed. In other cases no signs of an incipient hydrocephalus were definite until the fourth morning, and this may be considered to be the usual interval before the pathological change may be made out. Thus, aside from a sUght initial slowness in reaction, it may be assumed that no abnormalities are apparent until the lapse of sufficient time for the increase in intraventricular tension to cause enlargement of the head.

As soon as definite changes in the size of the anterior fontaneUe and in the widening of the sutures have appeared, the further enlargement of the head pro- gresses with a fair degree of rapidity'. In those kittens in wliich injection has not been made until after bon_y union of the cranium has occurred, there is a definite diastasis of the bones with the forming anew of fibrous sutures and fontaneUes. This opening-up of the bony skull has been observed in 5 kittens, the ages at the time of injection varjdng from 17 to 42 days. In general, however, these experi- ments have been performed on animals in which the closure of the skull was incom- plete; the enlargement of the head could be brought about by dilatation of the existing fibrous sutures.

Tliis enlargement of the head is of amazing rapidity and degree. In these experimental cases, as in man, the increase in size is practically entirely confined to the cranial vault, while the base of the skuU remains fairly constant. Such enlargement of the vault naturall^^ causes separation merely of the flat bones of the calvarium and leaves unchanged the relative positions of ej'es and ears.

The subsequent clinical course of the experimental kittens was largely influenced b}^ the factors mentioned. The weaker kittens soon reached a stage when the head became too heavy for them^ to Uft, so that progression was accom- pUshed by pushing the head along the floor of the cage. In others, the increasing weight of the head could be handled more easily, though most of these showed an ataxia more profound in degree than usual for kittens of equal age. ]\Iany of these kittens with enlarged heads remained very active even after two weeks; one in particular continued to cUmb with great facility upon the perpendicular wire side of the cage. In general, however, it must be granted that the kitten receiving the lampblack was more cautious and more sluggish in reaction than the control. The animals of the same litters subjected to subarachnoid or mtra ventricular injections of cinnabar could not be distinguished from normal.

The cause of death in the animals was variable, though two agencies were responsible for the majority. In the first place, death of the kittens from infection with B. hronchisepticus was unfortunately very common; the bronchial pneumonia

434 THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS.

from tliis organism affected many of the best litters. Again, the kittens with the unwieldy heads were unusually ai^t to fall and receive injury to the liead, etc. Others finally reached a point ai)parently when the increasing cerebro-spinal pres- sure affected the medullary centers.

The protocol of a typical experiment with injection of a suspension of lamp- black into the subarachnoid space of a kitten is given below:

Litter of 4 kittens (N3) born May 22, 1918.

When 20 days old (June 12, 1918) the whole litter was in excellent physical condition. Three of the litter were used for experimental injections and the fourth used as control. The history of one of the experimental animals (No. 41) and the control will be given.

The experimental kitten was on this day given ether and without shaving hair, punc- ture through the occipito-atlantoid ligament was done with release of about 0.5 c.c. clear cerebro-spinal fluid. Through this needle a subarachnoid injection of 1.0 c.c. Ringer's solution containing a 10 per cent suspension of lampblack was inade. At the time of injec- tion the fontanelles of all of the litter were closed and the whole skull bony, as determined by palpation. The litter was returned to mother.

On the next day (June 13) the experimental kitten was in excellent condition and its skull still tightly closed. The control was normal and active.

The second morning, however, a difference could be made out between the kittens. The experimental animal's cranial bones were definitely separated, but with a narrow fibrous interval. The control remained as before.

On the third day it was noted that the experimental kitten could not lift its head from the ground, though apparently in excellent physical condition. The animal revolved about its enlarged and hea\'y head as about a fixed point. The anterior fontanelle was extremely widely opened and the longitudinal and transverse sutures about 3 mm. wide.

This enlargement of the head continued, with the suture lines widening to 4 mm. and the fontanelle becoming still larger. The convexity of the calvarivim between the ears increased and the forehead became high and prominent. On the fifth day it was noted that the lower lid was being pulled up, covering the lower half of the pupil. The control animal i-emained normal and active, its skull remaining bony and enlarging as that of any normal animal.

On the eighth day the following notation regarding the experimental kitten was made: "Same excellent general condition. Head lias become very large and forehead is extremely prominent and high. Eyes are fast becoming obscured by the pulling-up of the lower lid; the sclera constantly shows as a white crescent above. Fontanelles and sutures are becom- ing Larger each day, bulging and protruding somewhat. The kitten can just lift its head up but a profoimd ataxia characterizes all movements. Can jirogress only by pushing its head along the ground." On the same day the control was recorded as "Excellent shape. Active. Fontanelles tightly closed; bony skull."

The animal continued to gain in strength and was able to raise its head and move around fairly readily though with considerable ataxixi. On the twelfth day it was noted that "from the glabella the forehead rises almost ])eniendicularly. The sutures are pal- pable from glabella posteriorly to occiput; laterally they nmy be traced far down under temples. All these suture-lines are from (i to 8 mm. wide while the fontanelle has a diameter of 10 mm." A photograph (fig. 11) of the animal on this day (June 24, 191S) is reproduced. Again, the next day, "Bony edges of the former calvarium are very ill defined and small. ^^^lole head seems soft and fibrous. Orbital ridge ;ilmost obliterated." The control remained normal.

Unfortimately the animal developed a very acute bronchise})ticus infection and was sacrificed, with the normal control, on the fourteenth day (June 20, 1918).

As the enlargement of the head is the most striking abnormality to be made out in the kitten during Ufe, a description of this anatomical change will be included. The first noticeable development, as already mentioned, is the alteration in the suture lines. The opening or enku"gement of a suture is usually to be demon- strated by gentle palpation; a definite increase in the cranial vault has been noted with certainty on gross inspection only after the fourth day, though before this time palpation gave good assurance of this increase. The enlargement of the head was usually made ob\dous by alteration in the angulations; this was due to the lack of associated expansion in the base of the skull. One of the first read- justments to tliis increase in size of the cranial ca-\dty was the elevation of the line of the forehead so that the profile rose abruptly from the line of the nose. This is shown in several figures (No. 11, from a kitten during Ufe, and also Nos. 6 and 9). In the normal kitten the Une of the skull in profile slopes backward in a very gentle angle of ascent, while the kitten wnth the intraspinous lampblack shows an increasingly abrupt rise to the forehead (fig. 9). In the course of about 2 weeks the enlargement of the vault is so great that on front A'iew the forehead seems to tower above the orbital ridge (figs. 5 and 6).

This increase in size of the vault -vvath marked elevation of the forehead is associated ^\^th other equally characteristic features. The elevation of the vault proceeds in these kittens so rapidly that the orbital ridge gradually seems dis- placed backward or obliterated (figs. 5 and 11). As the growth of the base of the skull proceeds as normally in these kittens, the increased intracranial tension continues to pull upward the restraining portions of the base. Laterally, however, over the ears, the whole vault bulges markedly' also and overhangs more prominently the bony canal (figs. 7 and 9). Here the bulging is more or less opposed to the retraction of the bony orbital ridge. The result of these forces is the rounding up of the whole cranial vault and to a lesser extent of the base of the skull, ^\dth an increase in the transverse diameter and a relatively smaller increase in the sagittal. This apparent rounding-up is shown in figures 10, 13, and 17.

These alterations in the shape and size of the cranium have other readjustments of the general appearance of the animal associated with them. Most striking of all is the general appearance of bulging of the whole head due to an increased con- vexity between ears and between occiput and glabella (cf. figs. 7 and 11). In the extreme cases the whole head may resemble the tj-pical "Turmschadel" noticed clinically in man. The ears seem in consequence to be placed at relatively low level in the skull on account of the fact that the enlargement has been wholly above the base (figs. 6 and 11).

Quite similarly caused is the pulling upward of the skin from the face and lower part of the head bj'^ the enlargement of the vault. This results in the typical white line of sclera showing above the iris and in the obscuring of the lower haK of the pupil by the lower lid. With the obUteration of the orbital ridge, the sclera beneath the retracted upper lid appears as a wide crescent, best to be seen from above because of the retracted orbital ridge. Tliis can be made out in figures 7 and 11.

From such findings and changes in the head, as givtm in the foregoing para- graphs, the diagnosis of an internal hydrocephakis in these kittens has been very easy during hfe. The kittens show practically every sign noted in the more chronic cases in children. Palpation of the head gives unmistakable evidence of fluctua- tion of a fluid; pathologically the diagnosis is confirmed. Examinations of the fundus of these kittens' eyes have been attempted but have not proved satis- factory. The control animals of the same Utter (subjected to no experimental pro- cedure) have shown no variation from the normal, nor have those other control animals, subjected to similar injections of other insoluble granules (usually cinna- bar, fig. 8). Thus each experimental kitten was controlled by an unoperated animal and by another in wliich analogous granules were injected. The relation of the injection of lam]:)black to the later occurrence of hydrocephalus seems estabUshed.

ADULT CATS.

All of the adult cats used in this series were given subarachnoid injections of lampblack through lumbar or occipito-atlantoid needle. No ventricular injections werc^ made, as interest was chiefly lodged in the production of hydrocephalus from intrameningeal injection. In all, 18 adult cats were subjected to such subarachnoid injections; of these, 12 received lampblack; 4 cinnabar; 1 lycopodium; and 1 "car- bon flour." Of the 12 receiving the regular lampblack, 4 died within the first 5 days after the experimental procedure. The longest period of survival after the injection was 22 days. On the other hand, the cat injected with "carbon flour" lived 4 months before being sacrificed, while the cat given lycopodium into the subarachnoid space was not killed until after 5 months. The cinnabar animals varied in length of life after injection from 3 daj^s to 2 months; most of these were sacrificed at the time when the lampblack animal in the same series died. Thus, the shorter period of survival in cats receiving lampblack as compared to others in the series is striking.

The difference in reaction of the cats to such subarachnoid injections, as com- pared to the kittens, can be made out by observation of the animals soon after injection. For the most part, signs of increased intracranial pressure were present the next morning after the injection; the animals would be lethargic, sleepy, and could not be roused. In the more profound cases the animals were found l.ying on their sides and finally went into coma. The onset of these signs of intracranial pressure frequently occurred within 12 hours; in all of the severe cases the phe- nomena were obvious within 24 hours. In such experiments, from the experience with kittens, it must be assumed that there is no possible enlargement of the cranial vault or other compensation for the acute increase in intracerebral pressure. The results, in consequence, are not as interesting or as striking as in the kitten, where compensation is possible.

Some of these adult cats with such an experimental, acute obstruction to the flow of cerebro-si)inal fluid went through a stage of marked cerebral excitation. The protocol of one such is given below, as it illustrates graphically the onset of the acute jjressure-increase and the later conversion into the stage of lethargy' and helplessness.

Protocol of Cat No. 99, adult male.

December 17, 1917, 10:35 a. m. Under ether anesthesia, occipito-atlantoid punc- ture, with release of about 1 c.c. clear cerebro-spinal fluid, was done. Slow subarach- noid injection through this needle of 5.0 c.c. of a 5 per cent suspension of Lampblack in Ringer's solution. Normal and rapid recovery from ether; animal walked about room within a few minutes.

One hour later (11:45 a. m.) animal was returned to cage, active and playful. Ran about as normal animal.

Six hours later (5 p. m.) cat was in same acti\'e, excellent condition. Ran about cage very rapidly.

Ten hours later (9 p. m.) the anunal was seen in a condition of cortical excitation. The movements were usually rotatory in character, though always associated with con- \Talsive retraction of neck. Epileptiform jactitation of all four legs and of the body. Cat can move about only in intervals of quiet between the attacks.

The next day (Dec. 18) the cat wasver>' lethargic and drowsy when undisturbed, but it could be stimulated to run, when it staggered considerably. It was noted, "quite a typical case of developing acute hydrocephalus."

Animal remained lethargic, slow, and sleepy, but was able to move about quite well if necessary. Quite inactive. On the sixth day the animal began to show a characteristic weakness and droop in the movements of his hind-legs, with a strange and rather ataxic lifting of the feet. Then after a few days (Dec. 29) the cat became "much more lethargic and wobbly, * * * no longer able to walk or struggle along. Lies on side in cage all of the time, weak and ataxic."

The cat did not recover from this condition, but became progressively worse and died on the sixteenth day (Jan. 2, 1918). It was injected with 10 per cent formalin through aorta and the brain removed for study. A photograph of transverse sections of this brain are gi\-en in figure 3.

This protocol gives the reaction of the animal to a rather small dose of lamp- black. Receiving only 5 c.c. of a 5 per cent suspension, it lived for 16 days, though showing typical signs of an increase in intracranial pressure (lethargy, ataxia, etc.). It has been found that if the concentration of the lampblack in suspension be increased to 10 per cent the hydrocephalus is more acute and striking. Such animals may go almost immediately through the stage of excitement, but show the signs of pressure on recovery from the anesthesia. This phenomenon of an acute increase in cerebral pressure seems the more likely to occur in older animals, though absolute data on this phase can not be had, as the ages of the cats used can be told only approximately. Obviously old cats (as judged by teeth, skin, activity, etc.) have not, as far as tliis impression holds, shown the same tendency to recovery noted in the young adult animals. To a far greater degree, the age-difference in reaction is brought out in the kittens, as already detailed.

These adult cats, then, after subarachnoid injection of suspensions of lamp- black, exhibit during life but Uttle of interest in their reactions. In general, the older animals show, within several hours, signs of disturbance of the intracranial pres- sure; some pass through a stage of excitement, but most of them become immedi- ately lethargic, weak, and ataxic. Some of these adult animals ma}- recover, after a couple of days, from the acute pressure changes and Uve for manj^ weeks as fairly normal animals. There is a striking difference in reaction after the injection, and due to this individuality no general rule can be formulated . The generaUzations recorded will remain more or less as impressions, but are of importance in the discussion.

One adult animal subjected to a subarachnoid injection of "carbon flour" (in which the granulation is quite coarse) showed really no clinical signs of acute cerebral pressure, but on being sacrificed after several months exhil^itod some enlargement of the lateral ventricles. Another cat was given a subarachnoid injection of lycopodium si)ores (sterilized by ])oiliiig). The cat remained normal and active for 6 months; it was then sacrificed for pathological control. No abnor- mahty existed except a widespread distribution of the lycopodium throughout the subarachnoid space (fig. 4). To further control the injection of granules in the subarachnoid space, several animals were given injections of cinnabar, similar in amount to those of lampblack. None of these animals showed any signs of increased intracranial pressure and, post mortem, no ventricular dilatation was present (fig. 2). Another animal was given repeated massive doses of the cinnabar into the sub- arachnoid space; the result of these repeated huge doses was a gradual abolition of function of the hind-legs, without signs of an increase in intracranial pressure. The peculiar power of the carbon granules in causing increased pressures within the central nervous sj^stem, with resulting hydrocephalus, seems therefore indicated.

GROSS PATHOLOGY OF THE CONDITION.

The diagnosis of the lesion of the central nervous system after the intraven- tricular or subarachnoid injection of lampblack, cinnabar and other particulate substances, naturally depends largely upon the pathological picture post mortem, though a good conception of the lesion may be had during hfe (especially in the kitten). In these experiments all of the animals were injected with 10 per cent formalin through the aorta and the tissues allowed to harden for some time before the; initial dissection and final immersion in formalin. The bony skull was then removed in the adults and the brain preserved with the dura intact. In kittens, however, due to the widely dilated sutures, etc., the brain was not removed, but was studied in situ in the skull by means of gross sections.

In both kittens and adult cats, in which intraventricular or subarachnoid injections of lampblack were made, the essential pathology of the central nervous system concerns a marked cUlatation of the lateral cerebral ventricles with altera- tions of the cortex, a typical internal hj'drocephalus. As the condition is quite different in the younger animals, as compared with the adults, the descriptions of the lesions will be given separately. Control animals, receiving similar injections of other granules, showed no abnormality of the central nervous system.

KITTENS.

The gross pathological lesion in the kittens surviving the intradural injection of lampblack for 10 days or over is practically identical in the different specimens. Reduced to simplest form, the al)normality consists in a tremendous and remark- able dilatation of the cerebral lateral ventricles (figs. 10, 14, 10). This increase in size of the lateral ventricles, associated with an enlargement of the kitten's head, results in a marked thinning of the cerebral cortc^x (figs. 10, 14, 16, and 20). In some of the cases the third ventricle seems obliterated by its marked enlargement and by the rearrangements of the walls of the interventricular foramina; in others the form of this ventricle is still left, though the whole structure has greatly increased in all of its dimensions (fig. 19). The underlying basal nuclei seem to survive this experimental increase in cerebro-spinal pressure most efficiently; their markings are still wholly visible in the basal view of the sectioned specimen (fig. 16). These general characteristics hold for practically all the specimens obtained. The whole process maj^ be likened to a partial reversion to the embryonic type of cerebral ventricle.

The essential feature of this experimental lesion (the dilatation of the cerebral ventricles) must be taken as the initial, direct result of the increased pressure of the cerebro-spinal fluid; this pressure is, in its turn, to be referred to the obUteration of certain of the pathways of the cerebro-spinal fluid and the consequent danoming back of the fluid. For, with the chief production of the fluid intraventricular (by choroid plexuses), and with the obstruction to flow distal to the tlurd ventricle, it seems but natural that the necessary readjustments should occur witliin the lateral ventricles. The initial mcrease in the size of these ventricles is the direct result of the increase in pressure, but the enormous dilatation (figs. 10, 14, and 16) met with in kittens is due to the potential distensibility of the head. This permits a tremendous increase in the size of the lateral ventricles, not possible under other conditions; and associated with this relatively extreme dilatation of the ventricles in kittens is the partial rounding-up of the different diverticula of the original cavities. Thus, the body and anterior horn of each lateral ventricle is early con- soUdated into a general, undifferentiated fluid-container; the posterior prolonga- tion is included at about the same time. The temporal cornu, running anteriorly toward the temporal pole, soon after shows evidence of enlargement in consequence of the increasing pressures, and then takes part in the general process of ventricular dilatation. The more extreme the enlargement, the more the distinction between the temporal prolongation and the main body of the lateral ventricles is ehminated. The net result of these alterations is that, on either coronal or transverse sections, the lateral ventricles, instead of appearing as mere shts as in the control or cinnabar kittens (fig. 10), seem to occupy, with their content of cerebro-spinal fluid, the major portion of the kitten's cranial cavity (figs. 10 and 20).

The thinning of the cerebral cortex is as remarkable and as extreme as the dilatation of the ventricles. Normally, the gray and white matter of the cortex practically fills the cranial chamber, with the exception of the narrow shts of the ventricles. This is shown in gross in the normal control animals in figures 10, 19, and 20. In the kittens receiving either intraventricular or subarachnoid injections of lampblack the cortex becomes, within 10 days, reduced to a thin sheet of nervous tissue 1 to 4 mm. in thickness. For the most part the extreme reduction in thick- ness is in the parietal and adjacent areas; around the temporal or frontal poles, resting on the more or less fixed portion of the skull, the thinning out of cortex may not be so extreme, though some cases show marked tliinning of temporal cortex. This reduction of cortex is striking, and it is remarkable that any cerebral function, as judged by the imperfect activity of the aninuil, should persist. In such a thinned cortex it is quite difficult to distinguish between the gray and white matter. It seems, on gross appearance, that the remaining portion of the brain tissue is com- posed largely of fibers and that the nerve cells are spread out and condensed into a very narrow zone beneath the pia, rendering macroscopic identification difficult in the formalinized preparation.

In practically all of the more pronounced hydrocephalics the basal ganglia may be made out on examination of the inferior surface of the ventricles from above. The same picture of prominent masses of the gangha is shown on coronal section, but the best views are afforded in the specimens in which the top of the cranium has been removed by a transverse cut. The general appearance of these masses is given in figure 16, from a kitten which was sacrificed 22 days after a subarachnoid injection of 1 c.c. of a 10 per cent suspension of lampblack. On each side two rounded masses project into the enormously dilated ventricles; these represent the more or less undisturbed nucleus caudatus and nucleus lentiformis. The thalamus is obscured somewhat in a gentle swelUng in the medial portion of each hemisphere. The dislocation of these nuclear masses is not marked, for they are an integral part of the brain tissue in approximation to the base of the skull ; changes here are much less pronounced than in the vertex. Quite similar to this survival of the basal gangha is the isolation (on development of an internal hydrocephalus) of the fiber bundles of the fornix, for these maintain a strand-Hke jjrolongation on the floor of these dilated ventricles. Other fiber-bundles hkewise can be made out, dislocated to a greater or lesser extent in the enlargement of the third and lateral ventricles. Such a i)ushing-back holds for the fibers of the corpus callosum (fig. 20).

There is no essential difference between the internal hydrocephalus produced by intraventricular injection of lamjiblack and that produced by subarachnoid. Record has been made of minor thfferences, such as the more or less extensive obliteration of the tliird ventricle and of the septum pellucidum in tlie direct intraventricular injections, as compared to the partial survival of these structures in the subarachnoid type. Most marked of all the differentiations, however, is the variation in the distribution of the carbon granules found at autopsy. In the kitten receiving ventricular injection a dense black layer of granules obscuring the picture is customarily' found in the basal regions of the dilated cerebi'ul ventricles (fig. 10). In the upper half of the cavity, however, the amount of lampblack is much less. Quite unUke this is the much smaller amount of carbon visible in the dilated ventricles of kittens injected by the subarachnoid route. In these, collec- tions of granules, scattered and small in amoimt, are the usual findings in the ventricular floor (as in fig. 10), but in some of the specimens the walls of the ven- tricles are obscured by a dejjosit giving in the gross a brownish tint.

An interesting f(;ature of the i)artial obhteration of the basal markings by the dense layer of carbon granules in such intraventricular injections concerns the rela- tions of the choroid plexus. This appears, in the formalin specimen, as a delicate filament in each ventricle, only slightly obscured by the lam])black. These plexuses in some si)ecimens remain fairly free from such carbon deposition, probably due to the constant secretion of fluid by the cells and the consequent washing-off of any lodging particles. On this hypothesis, which seems justified, the production of cerebro-spinal fluid by the ependyma must be neghgible.

The gross pathological features, then, of the central nervous system of a kitten receiving intradural injection of lampblack are those of a tj^pical internal hydro- cephalus, such as is cUnically quite conmion in children. The dilatation of the cerebral ventricles thus produced e.xperimentally has been extreme.

ADULT CATS.

The same pathological dilatation of the lateral ventricles has been produced by this means in adult animals, but the degree of dilatation is far less than in kittens. This is in large part to be accounted for by the fact that in these adult animals enlargement of the bony skull is impossible and the compression of the cortex, through dilatation of the ventricles, is associated with the physiological limit of increase in intracranial pressure and its consequent bulbar effects. Bitem- poral decompressions might possibly allow greater ventricular enlargement and a longer period of survival for the animal.

But by such injections of lampblack an obvious and considerable dilatation of the lateral ventricles is effected (figs. 1 and 3). The lateral ventricles in the most extreme cases have become dilated to 7 to 8 mm. in transverse diameter — an enlargement comparable to those illustrated by Thomas (1914) and by Dandy and Blackfan (1913, 1914), though occurring in a shorter period. The dilatation is for the most part a sj-mmetrical process and is confined at first, or in the less extreme cases, to the body and frontal prolongation of the ca\'ity. In the more striking cases the temporal prolongation is found dilated and the enlargement is traceable into the posterior horn. Such changes in ventricular capacity are whollj- similar to the internal hydrocephalus developing cUnically in man after obstruction to the pathways of the cerebro-spinal fluid. One receives the impression that the changes in the very old cats are not as marked as those occurring in the young adults.

The thinning of the cortex in these adults is, of course, not marked, and is dependent upon the dilatation of the ventricles; for the reduction in thickness of the cortex is not, under these experimental conditions, in any way primary but is second- ary. The differentiation between gray and white matter is not lost, even in these formaUnized specimens (fig. 3).

In the adult animals the suspension of lampblack, when introduced into the cisterna cerebello-medullaris by occipito-atlantoid puncture, finds its way into the lateral ventricles in rather small amounts. The chief distribution of the granules after such injection is into the spinal and basilar subarachnoid spaces. The lamp- black after a massive injection is found frequently in rather large amount in the temporal process of the lateral ventricle; in these cases the dilatation has not been great. The comjjarative freedom of the choroid plexuses from the granules, pointed out in kittens, has been noted in the adults.

Pathologically, the degree of dilatation of the lateral ventricles following subarachnoid injections of lampblack has been somewhat variable (cf. figs. 1 and 3).

A moderate injection of a 10 per cent susijension yielded in 5 days considerable ventricular enlargement (fig. 1), while the 5 per cent suspension gave in 16 daj's but Uttle (fig. 3). Comparable subarachnoid injections of cinnabar and of lyco- podium spores caused no obvious abnormality in ventricular capacity (figs. 2 and 4).

DISCUSSION OF RESULTS.

The production of a typical internal hydrocephalus in kittens and adult cats by the injection of lampblack into the normal pathways of the cerebro-sjjinal fluid invites question as to the exact mechanism by which this enlargement of the ventricles is brought about. In both kittens and adult cats the condition has been caused by the injection of a suspension of these carbon granules through the occipito- atlantoid ligament into the cisterna cerebello-medullaris. The distribution of these granules subsequently is largely within the basilar and spinal subarachnoid space, with a smaller spread over the cerebral and cerebellar cortices. The maximal aggregation of granules is in the peribulbar cisterns with a minimal concentration within the ventricles. Following the intraventricular injection, as used in some of these kittens, the distribution of granules is largely intraventricular, basilar, and spinal, with but a small amount over the cerebrum. The same pathological picture in the main results from both types of injection.

After such experimental procedures there is usually a distinct interval of time between the initial injection and the appearance of signs indicative of intracrania pressure. In adult cats, this interval is usually of 6 or more hours. In very old cats, however, there seems to be really no time interval; the obstruction to flow seems complete enough to induce immediately a state of lethargy. This interval in kittens, however, is prolonged to 24 hours or more; usually enlargement of the head can be noted only after the fourth day.

It becomes necessary to reconcile, if possible, these somewhat divergent time- intervals and to attempt the formulation of an hypothesis to meet the conditions. The almost immediate appearance of a lethargy in very old cats indicates that at least a partial obstruction of the cerebro-spinal fluid is caused by the mere col- lection of these granules in the subarachnoid space. The fact that these older animals show symptoms immediately may be due to a decrease in the power of the medulla to resist alterations in pressure in the subarachnoid space. The increase in this pressure must be acute in all of the animals, but it seems likely that the obstruc- tion to flow is only partial and that with a sUghtly increased head of pressure the fluid is forced through the incompletely occluded channels.

8ubse(}uently, another factor seems to play a role and the blockage becomes apparently more complete. Two explanations for the formation of this obstruction may be off'ered: The first concerns the definite aggregation of the granules into a fairly imi)ervious, impenetrable mass, mechanically hindcM'ing the flow of cerebro- spinal fluid. This probably plays a part in the initial blocking of the channels, but some other influence is doubtless necessary to render the aggregation of granules more impervious to fluid. This second factor is very likely the reactiv(> phenomenon on the part of the body to the presence of such foreign granulation. Such a reaction may be considered inflammatory, with more or less rapid deposition of fibrin and possibly the arousing of the fixed tissue-cells in the neighborhood. The reaction of the cells lining the subarachnoid spaces to the presence of carbon granules has already been noted (Weed, 1917). It may be assumed, then, that the block to flow of the cerebro-spinal fluid is dependent upon an aggregation of the granules into an impervious mass, the process probably being faciUtated and the block perfected by the inflammatory reaction.

Question immediately arises as to the possible explanation of the failure of cinnabar and other granules, when injected in similar amounts into the cerebral ventricles and into the subarachnoid space, to give rise to internal hydrocephalus. This failure seems best explained by the assumption that these granules are not able to form as efficient aggregations even after the inflammatory reaction, so that the flow of the cerebro-spinal fluid is not impeded. This seems the more surprising for such a substance as lycoj^odium. With the cinnabar a minimal toxicity may modify the necessary inflammatory reaction.

It is quite difficult, after such injections of foreign particulate matter, to deter- mine the exact point of obstruction to the flow of the cerebro-spinal fluid. The fact that similar pictures may be produced by intraventricular and by subarach- noid injections of lampblack indicates that in general a similar area of obstruction exists. Consideration of the density and distribution of the granules at autopsy inclines one to the view that the obstruction is primarily meningeal in character, and is probably a somewhat diffuse process in the basilar and possibly in the cortical portions of the subarachnoid space. The gross accumulation of granules occupies a portion of the cisterna cerebello-medullaris and the smaller cisterns of the base of the brain, but the mesh of the subarachnoid space is here of the maximum. To block this widened mesh completely seems more difficult than to do so in the cor- tical portion of the si:)ace, where the mesh is very fine and where a few granules and a reactive inflammatory process seem to have greater facilities for effecting a block- age of the channels for the cerebro-spinal fluid. It is very difficult to determine with certainty the ultimate obstruction to flow in these channels, but it must be considered as a diffuse intrameningeal i^rocess, whether in the basilar regions, or over the cortex, or about the various dural venous sinuses. The explanation, in these experimental animals as in man, for such obstruction to the flow of cerebro- spinal fluid through the meninges can not yet be given.

With the intrameningeal block of marked efficacy, the acute reduction of thickness of the cerebral cortex does not seem so remarkable. With such thinning to a very few milUmeters, there is a possibiUty of two processes taking part. First, the thinning may be largely due to actual compression or destruction of brain- tissue. That tliis plays an important part in the enlargement of the ventricles in adults, where the cranial volume is fixed, must be granted; also, in cases of an infec- tive hydrocephalus the two factors of compression and destruction work together. In the kittens, however, where the cranial capacity may be enlarged, the latter factor does not play the essential role. This is demonstrated by such findings as the retention (in the process of dilatation of the ventricles and thinning of the cortex) of practically all of the essential intraventricular markings and structures; these are altered somewhat by the dilatation of the ventricles but remain easily identified. It must be granted, then, that the thinning of cerebral cortex in such internal hydrocephalus is the result largely of a rearrangement of tissues — ^a stretch- ing and compression of the existing brain-tissue to cover the enlarging ventricles. In this enlargement some destruction of tissue may take place, but the essential process is a rearrangement of the bulk of cerebral tissue.

The obstruction to flow of the cerebro-spinal fluid, brought about by intra- ventricular or subarachnoid injection of lampblack, must be assumed, then, to be due to aggregation of these granules into an impervious mass, the essential and ultimate matting together being accomplished probably by an inflammatory pro- cess. Because of this obstruction, enlargement of the lateral ventricles follows, necessitating a diminution in thickness of the cortex cerebri, brought about by some tissue compression (as in adults) and by compression and readjustment of brain bulk (as in kittens).

SUMMARY.

An acute internal hydrocephalus may be produced by the intraventricular or subarachnoid injection of suitable amounts of a suspension of lampblack. In kittens the degree of this internal hj'drocephalus is extreme, being associated with a marked enlargement of the head and other changes in the general appearance. This extreme dilatation of the ventricles with thinning of the cerebral cortex in kittens has been brought about in 10 days. In adult animals a similar dilatation of the lateral ventricles, but of lesser degree, may be caused by the same procedure. The internal hydrocephalus, produced experimentally in this way, is comparable in detail to similar conditions in man.

BIBLIOGRAPHY.

Burr, C. W., and D. J. McCarthy, 1900. Acute inter- nal hydrocephalus. A clinical and pathological study. Jour. Exp. Med., vol. 5, p. 195.

Gushing, H., 1908. Surgery of Head. In Keen's Sur- gery, vol. 3, p. 17-206.

Dandy, VV. E., and K. D. Blackfan, 1913. An experi- mental and clinical study of internal hydrocepha- lus. Jour. Am. Med. A.ssoc, vol. 61, p. 2,216.

, 1914. Internal hydrocephalus: an experimental,

clinical and pathological study. Am. Jour. Diseases of Children, vol. 8, p. 406.

, 1917. Internal hydrocephalus — second paper.

Amer. Jour. Diseases of Children, vol. 14, p. 424.

Faivre, J. J. a. E., 18.53. Des granulationes mfiningiennes. These de Paris.

Flexner, S., 1907. Experimental cerebro-spinal men- ingitis in monkeys. Jour. Exp. Med., vol. 9, p. 142.

Key, G. and A., Retzics, 1876. Anatomie des Ner- vensystems und des Bindesgewebe. Stockholm.

LuscHKA, H., 1855. Die Adergefiechte des menschlichen Gehirns. Berlin.

MoTT, F. W., 1910. The Oliver-Sharpey lectures on the cerebro-spinal fluid. Lancet, Part 2, p. 1 and p. 79.

Thomas, W. S., 1914. Experimental hydrocephalus. Jour. Exper. Med., vol. 19, p. 106.

Weed, L. H., 1914a. Studies on cerebro-spinal fluid, No. II. The theories of drainage of cerebro- spinal fluid with an analysis of the methods of investigation. Jour. Med. Research, vol. 31 (n. s. 26), p. 21.

, 19146. Studies on cerebro-spinal fluid. No. iii.

The pathways of escape from the subarachnoid spaces with particular reference to the arachnoid villi. Jour. Med. Research, vol. 31 (n. s. 26), p. 51.

, 1914c. Studies on cerebro-spinal fluid. No. iv.

The dual source of cerebro-spinal fluid. Jour. Med. Research, vol. 31 (n. s. 26), p. 93.

, 1916a. The establishment of the circulation of

the cerebro-spinal fluid. Anat. Rec, vol. 10, p. 256.

, 19166. The formation of the cranial subarach- noid spaces. Anat. Rec, vol. 10, p. 475.

, 1917. The development of the cerebro-spinal

spaces in pig and in man. Contributions to Embrj'ologj', No. 14. Carnegie Inst. Wash., Pub. No. 225.

EXPLANATION OF FIGURES.

Fig. 1. Photograph of two transverse sections of adult cat's brain (No. 90). The animal was given a subarachnoid injection of 5.0 c.c. of a 10 per cent suspension of lampblack in Ringer's solution and immediately afterwards exhibited signs of cortical excitation. Within 2 hours it became lethargic and could not be roused. It remained in this condition for 4 days and died on the morning of the fifth day. Considerable dilatation of lateral ventricles is shown.

Fio. 2. Photograph of two transverse sections ol adult cat's brain (No. 103). By occipito-atlantoid puncture, the animal was given a subarachnoid injection of 5.0 c.c. of a 10 per cent suspension of cinnabar in Ringer's solution. Animal remained normal and active, without sign of increase m intracranial pressure, for 8 days; it then developed distemper and died on the tenth day. No abnormaUties in lateral ventricles are shown.

Fig. 3. Photograph of two transverse sections of adult cat's brain (No. 99). Animal was given subarachnoid injec- tion of 5.0 c.c. of a 5 per cent suspension of lampblack in Ringer's solution. Ten hours after animal went through stage of excitement, then became lethargic and slow; showed signs of a subacute increase in intra- cranial pressure and died on the sixteenth day. Full protocol in te.xt. Sliglit enlargement of lateral ven- tricles is shown.

Fig. 4. Photograph of a tj-pical transverse section of the brain of an adult cat (No. 100). In this animal 5.0 c.c. of a 5 per cent suspension of lycopodium in Ringer's solution was injected into the subarachnoid space. Animal showed no signs of any increase in intracranial tension; it was normal and active. At end of 6 months it was sacrificed. The lateral ventricles appear as normally.

Fig. 5. Photograph, during life, of a kitten receiving two intraventricular injections of 1.0 c.c. of a 5 per cent suspen- sion of lampblack, 11 days apart. Following the first injection some ventricular dilation occurred, but after the second the process of enlargement was rapid. Photograph was taken on thirty-fourth day. Animal was sacrificed on the forty-sixth day after the first injection.

Fig. 6. Photograph, taken immediately after death, of a kitten which when 9 days old was given intraventricular injection of 1.0 c.c. of a 10 per cent suspension of lampblack in normal salt solution. Animal Uved for 14 days and was then sacrificed.

Fig. 7. Photograph, taken immediately after death, of a kitten (Litter Ej) which at age of 7 days received intraven- tricular injection of 1.0 c.c. of a 5 per cent suspension of lampblack in normal saline. After 15 days, received similar injection of 1.0 c.c. of a 10 per cent suspension; at this time it was noted that the fontanelles were opening. Subsequently the head enlarged rapidly and animal was sacrificed on the thirt}--seventh day. Compare figure 6.

Fig. 8. Photograph, taken immediately after death, of a kitten (Litter Ej) which when 1, 7, and 22 days old received subarachnoid injections of 1.0 c.c. of 5 per cent suspension of cinnabar each. No abnormality in devel- opment or actions noted. Sacrificed on thirty-seventh day.

446

EXPLANATION OF FIGURES.

Fio. 9. Lateral vii'ws of skulls of three kittens from sMiuc litter (F;). Tlieaniiii:ds were all sacrifieed on the twenty- seventh day aftei" the exporimental proeedure. The skull to the right is that of the control to whieh no injections were given. On the left is the skull of the kitten which received an intraventricular injection of 1.0 c.c. of a 5 per cent sasjiension of cinnabar. No change from th(^ normal was noted in tliis kitten during life; at autopsy the skull was completely closed by bony union, as was the control's. In the center is the skull of the tliiid kitten wliieh received when 4 days old 1.0 c.c. of a 5 per cent suspension of lampblack. Tj'pical internal hydrocephalus resulted.

Fig. 10. Photograi)h of sectioned heads of same kittens as shown in figure 9. The skull-cap and underlying brain have been removed in same way from each. On the right is the control kitten; on the left is that of the kitten receiving intraventricular cinnabar. In the center is the hydrocephalic kitten which was given the intra- ventricular injection of lampblack.

Fk:. 1 1 . Photograph during life of a kitten which received a subarachnoid injection of 1.0 c.c. of a 10 per cent saspen- sion of lampblack, when 20 days old and when skull was closed. Photograph was taken on twelfth day after the injection. Full jMotocol of animal in text.

Fk;. 12. Lateral views of skulls of two kittens from same litter (Nj). Above is the skull of the control animal while below is that of the same kitten as in figiu'e 11. After receiving subarachnoid injection of lampblack, kitten lived 1.5 days; control was killed on same day.

Fro. 1.3. Photograph of skulls of same kittens as given in figure 12. The control appears to the right, hydrocephalic on the left.

Fig. 14. Photograph of sectioned heads of same kittens as recorded in figure 12. On the right is the control; on the left is the head of the kitten receiving subaraclinoid injection of lampblack (cf. fig. 11).

Fig. 1.5. Lateral view of skulLs of two kittens from same litter (Oj). On the right is the control; on the left is the skull of kitten receiving subarachnoid injection of 1.0 c.c. of a 10 per cent suspension of lampblack. At time of injection this kitten was 10 days old. Animal developed a typical hydrocephalus and was sacri- ficed with control on the twenty-second day after injection.

Fig. 16. Photograph of sectioned heads of same kittens as in figure 15; on the right is the control, on the left is the hydrocephahc. The carbon granules occurring on the ventricular floor are typical of the deposit which occurs after such subarachnoid injection.

Fig. 17. Photograph from above of skulls of two kittens from same litter (J2). On the right is that of the control animal, on the left is that of the experimental animal. This kitten when 42 days old was given a subarach- noid injection 1.0 c.c. of 5 per cent of lampblack in normal saline. The skull wliieh was previously tightly closed opened up and wide suture lines were formed. Sacrificed, with control, on twenty-first day after injection.

Fig. 18. Lateral view of same skulls as reproduced in figure 17. The control is below, the experimental hydrocephalic above.

Fig. 19. Photograph of transversely sectioned skulls of same kittens as in figures 17 and 18; photograph taken from behind, looking toward nose. On the right is the control; on the left the experimental animal, showing resulting internal hydrocephalus.

Fig. 20. Photograph of sectioned heads as in figure 19, taken looking toward the occiput. The enlargement of tem- poral cornua of lateral ventricles is shown.