Book - Contributions to Embryology Carnegie Institution No.53

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Barry LW. The effects of inanition in the pregnant albino rat with special reference to the changes in the relative weights of the various parts, systems, and organs of the offspring. (1920) Contrib. Embryol., Carnegie Inst. Wash. 91-136

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This historic 1920 paper describes the effects of inanition, a restriction of the maternal diet causing a lack of nourishment, on rat development.



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The Effects of Inanition in the Pregnant Albino Rat

with special reference to the changes in the relative weights of the various parts, systems, and organs of the offspring.


By Lee Willis Barry, M. D., Ph. D.

Of the Departments of Obstetrics ami Gynecology and of Anatomy, University of Minnesota.


Introduction

That a restriction of the diet of the mother during pregnancy usually results in a decrease in the weight of the offspring has long been known. Prochownick (1899, 1901) obtained a marked reduction in the weight of the human newborn by a restriction of the mother's diet during the last weeks of pregnancy. Rudolski (1893) starved rabbits and a dog during pregnancy and noted a reduction in the size of the offspring. Paton (1903) underfed pregnant guinea-pigs and obtained a marked reduction in the weight of the young. Reeb (1905) underfed rabbits and dogs during pregnancy and obtained young greatly reduced in weight. However, none of the above made any observations upon the changes in the relative weights of the various organs, systems, and parts of the newborn which might occur during inanition of the pregnant mother. The main object of this investigation, therefore, is to show the effect of inanition in the pregnant albino rat upon the changes in the relative weights of the various systems, organs, and parts of her newborn. Observations were made also on the possibility of blighting of the ovum, death of the fetus in utero, prolongation of gestation, abortions, and premature deliveries during inanition of the mother.

The work was done in the Departments of Obstetrics and of Anatomy of the University of Minnesota, under the supervision of Doctors J. C Litzenberg and C. M. Jackson, to whom I am deeply indebted for valuable aid and suggestions.

Materials and methods

For the present investigations, two series of adult female rats (Mus norvegicus albinus) were used for inanition during pregnancy. Those in series A are adult females from the colony at the Institute of Anatomy, which were kindly given over to my use by Dr. C. M. Jackson; Series B consists of adult females from several sources. A few were reared from normal litters in Series A; some were purchased from a local animal dealer, and others were obtained from the departments of Physiology and Psychology of the University. Unfortunately, however, the exact age of very few of the females was known.

Breeding

Since the influence of inanition on the length of gestation was to be noted, and in order to exclude the possibility of some of the small rats being the result of premature birth, it was very important to know the approximate date of copulation.

Three methods were used:

(1) Kirkham and Burr (1913) have shown that the female albino rat usually ovulates within 20 to 48 hours after the birth of a litter, and impregnation occurs 1 to 4 days after the casting of a litter. A few of my females became pregnant by this method, the males being left with the mother during the second night following delivery. This method was abandoned, however, since out of a very large number of females delivering only a few became pregnant.

(2) The second method was to place several males alone in small wire cages and once each day the different females were placed with the males. If the female was in heat, copulation usually took place at once. The female was not removed at once, but was left with the male for a period varying from 15 minutes to an hour. If not in heat, the female usually resented the advances of the male, in which case ehe was removed and replaced by another female. After successful pairing with the male, the female was weighed. Her weight, together with her number, was recorded, and she was placed in a cage with other females that had paired. It was found better to place the female in with the male, because when the process was reversed the male, suddenly finding himself thrust into a strange cage, paid very scant attention to the female, but would spend all his time attempting to escape from the strange cage. The majority of the females were paired by this method.

(3) The third method employed consisted in placing several males in a cage with a number of females. They were left together constantly and inspected at intervals of 6 hours during the day and once, in the evening. When a female in the cage became in heat, the males would copulate with her with such frequency that in a short time the vagina became distended, reddened, and at times would bleed slightly. After a little experience, one can readily distinguish the females that have copulated by the distended, reddened, and at times slightly bloody vaginal orifice.

Period and severity of starvation

In the beginning of the investigations it was decided to starve one group of females throughout pregnancy and another group during the last half only. The results from starvation were so disappointing that this part was abandoned. Of 17 females that had been observed to copulate and were starved from this time for periods varying from 16 to 26 days, only one female gave birth to a litter, 4 of the 17 died, and the others were so weakened that they were saved only with difficulty. In the second group 59 females were starved severely during the last half of pregnancy (or suspected pregnancy), beginning on the eleventh day after copulation. The animals were weighed daily and their weights recorded. The amount of food (usually not more than 1 gram) which they received daily varied with their loss in weight and general condition. The food consisted of whole-wheat bread (Graham) soaked in whole milk. (See table 1 for amount of food given each female during starvation.) Water from the city supply was allowed in the cages at all times.

Preventing the mothers from eating their young

A difficulty soon experienced was the eating of the young by the starving mothers. Early in the investigation several of the mothers ate and mutilated their newborn young, rendering them worthless for dissection purposes. Various muzzles were devised but without success. The method finally adopted was to place the pregnant female in a cage with a wire bottom, the meshes of which were 1 em. square, thus allowing the newborn rats to drop through onto a clean piece of paper beneath. Thus, not only were the newborns saved for dissection, but any abortions or premature deliveries might be noted.


Throughout the period of inanition the pregnant females were kept in a specially warmed room in order to prevent death from chilling or pneumonia.

Autopsies

In this investigation 99 rats were autopsied, GO of which were from mothers underfed during the last half of pregnancy, 29 were normal fetuses removed from the recently killed mother, and 10 were normal newborns. In order to compare the effect of prenatal inanition in the newborn rat (test), it was necessary to compare this test rat with a normal (control) fetus of the same body-weight from an unstarved mother.

The mothers from which the control fetuses were obtained were chloroformed. After death the abdomen was slit open and the fetuses and placentae removed from the uterine horns. The fetus was removed from the amniotic sac and the umbilical cord severed by crushing in order to prevent bleeding, close to the belly wall. The fetus was quickly wiped dry of excess fluid, killed by chloroform, measured, weighed, and dissected. These are. designated the "prenatal controls." The "test rats" are newborn rats from the underfed mothers. The "normal newborns" are newborn rats from normal litters.

The series and number of the mother, the number of the litter, and the order in the litter for each individual dissected is shown in table 4. A or B with the number following denote the series and number of the mother in the series; the number following this denotes the number of litters the mother has borne during the experiment, while the number following the decimal point denotes the number of the individual rat in the litter. For example, B2-2.1 would show that the rat was number 1 in the second litter from the mother number 2, Series B.

It will be noted that these rats (table 4) are arranged in five groups in accordance with their net body-weights. Group 1 contains the test rats and prenatal controls whose net body-weights range from approximately 2 to 2.5 grams; Group II, those ranging from 2.5 to 3 grams; Group III, those ranging from 3 to 3.5 grams; Group IV, those ranging from 3.5 to 4 grams, and Group V, those ranging from 4 to 4.5 grams. This grouping was done in order to facilitate computations and t<> render apparent any variations according to the size of the rats. Since no sexual differences were found in the organs and parts, the sexes are combined in the groups and -computations. All computations were made on the average weights of the organs and parts. The original individual data will be filed at the Wistar Institute of Anatomy, Philadelphia, where they will be available for reference.

All the test rats autopsied were born by the natural method, although the length of gestation was occasionally prolonged.

The autopsy technique used was the same as that described by Jackson and Lowery (1912) and Jackson (1913), with a few modifications. Their technique was as follows: After killing with chloroform, the gross body-weight and lengths of body (nose-anus) and tail were recorded. The head was removed on a plane just anterior to the larnyx and posterior to the cranium, and weighed. The trunk was suspended, thus allowing the blood (unmeasured) to escape. The eyeballs and brain were then removed and placed in a moist chamber. The trunk was next dissected and the viscera removed and weighed individually in the following sequence: thyroid gland, thymus, heart (opened and blood clots removed), lungs, liver, spleen, stomach and intestines (including contents, mesentery and pancreas, also weighed without contents), suprarenals, kidneys, gonads, and spinal cord.

The extremities were removed at the shoulder and hip joints and weighed. The skin was next removed from the trunk and extremities and weighed; the skeleton and musculature were weighed together; then the musculature was dissected off and its weight determined by subtracting the weight of the skeleton from the combined weight.

As soon as possible after birth of the inanition test-rats, and immediately after the removal of the prenatal controls from the mother, they were killed by chloroform, if not already dead. Each was then placed upon its back and extended by allowing one end of a steel ruler (300 by 35 by 2 mm., weight 263.5 grams) to rest upon the abdomen and neck. In this way the amount of extension was found to be much more constant than by trying to hold the body extended by means of the hand.

The distance from the tip of the nose to the anus (nose-anus length) and from the tip of the tail to the anus (tail-length) was carefully measured by calipers and the distance read off on a millimeter scale.

Jackson and Lowrey weighed the stomach, intestines, and pancreas together with mesentery. In my investigation, however, the stomach, intestines, and pancreas were weighed separately. The technique was as follows: The rat was placed belly down and the skin, muscles, and other tissues dissected from the left lumbar region and an incision made through the peritoneum just below the costal margin. By gentle pressure upon the abdomen, the stomach, spleen, and part of the pancreas were forced through the opening. The spleen was now easily separated from the stomach and pancreas and placed in a moist chamber. The stomach was then freed from its attachments to the liver and pancreas, seized at its junction with the esophagus with a small pair of forceps, firmly compressed to prevent the escape of any of the gastric contents, and severed at that point and also at the pylorus. The stomach was then weighed in a closed container, opened, its contents allowed to escape, and the interior cleaned with moist filter paper, after which it was reweighed. The intestines were removed as described by Jackson and Lowrey (1912) and weighed with and without their contents, after the pancreas had been removed. By subtracting the weight of the contents from the body-weight, the net bodyweight was obtained, and this was used as a basis for computations.

It was found that the "gold dust" preparation, used by Jackson (1915) to tree the skeleton of its periosteum and ligaments, acted too strongly upon the delicate skeletons in my series, resulting in a loss of the cartilages. Consequently, the skeletons were cleaned as thoroughly as possible of muscles and ligaments merely by dissection. These are designated as "moist" skeletons. The moist skeletons were dried for 1 month (to a constant weight) in an oven at a temperature of 85° to 95° C. to obtain their dry weight.

General effects of underfeeding

Blighting of ovum

In one experiment 17 female albino rats were underfed for varying periods of 16 to 26 days from the time of observed copulation. Only 1 (A 6) gave birth to a litter after 24 days. This mother received daily 10 grams of food until the eleventh day after copulation, and thereafter 1 gram daily until delivery, starvation being severe only in the last halt of pregnancy. Her fetuses were autopsicd and included with the data. Of the 17 rats, 4 died of starvation. Autopsy revealed no pneumonia or other disease.

In another series 59 females were underfed from the eleventh day after copulation to delivery, death, or the discovery of no existing pregnancy. Of this number, 19 (table 1), or 32 per cent, gave birth to litters; 12, or 20 per cent, died during pregnancy (table 2) ; and 27, or 46 per cent, did not give birth to litters (table 3) .

Huber (1915) found that in the rat, on the sixth day after copulation, localized thickenings of

the uterine mucosa, sufficient to cause localized swellings of the uterine tube, were evident. Stotsenburg (1915) has shown that on the thirteenth day of pregnancy the average weight of the rat fetus is 0.040 gram. It is interesting to note that in my pregnant rats it was found that the swellings in the uterine horns could be palpated through the abdominal wall of the living animal between the tenth and eleventh days after copulation. None of the females (16 in number) underfed from the time of copulation, and not having litters, showed swellings in the uterine horns at any time palpable through the abdominal wall. In the 27 females (table 3) observed to copulate and underfed from the eleventh day thereafter (no litters resulting), swellings in the uterine horns were palpated in 15 cases, doubtful in 3, and not palpable in 9. Of the 27 animals, 5 died during the starvation period; 4 of these were autopsied, 1 (A 63) showing definite swellings in the uterine horns (2 in right, 3 in left, about 8 mm. in diameter), the other three showing no macroscopic evidence of pregnancy.

[Microscopic examination of sections of the uterine swellings (in A 63) revealed a mass of degenerating tissue with no evidence of any fetus. One female (B 64) was refed 10 days (after being underfed 12 days) and killed. At autopsy 4 swellings in the left and 5 in the right uterine horn were found, averaging about 1 cm. in diameter. Microscopic examination of these showed a mass of degenerating tissue with no evidences of any fetal tissue. Apparently these were cases of blighted ova or early embryos. What was the fate of the swelling palpated in the other rats starved? Were they absorbed? This question needs further investigation.

It is significant to note that of the 17 females starved from the time of copulation, only one became visibly pregnant and no swellings were ever palpated in the remaining 16. Does starvation early in pregnancy inhibit implantation by lessening the amount of pabulum or embryotroph necessary to the nourishment of the ovum, or by uterine circulatory changes or a condition of acidosis? Or does it cause a blighting of the ovum after implantation? This also needs further investigation.


Length of gestation

According to Stotsenburg (1914), the length of gestation in the non-lactating albino rat varies from 21 days and 15 hours to 22 days and 16 hours. The length of gestation in my starved mothers varied from 21 to 26 days; 8 of the 22 total are above the 23-day limit— 6 with a gestation-period of 24 days, 1 of 29, 1 of 26. Thus, severe inanition during the last half of pregnancy usually lengthens the duration of gestation comparatively little. This is rather surprising, in view of the fact that King (1913) found the gestation period markedly lengthened in pregnant nursing rats. King says:

"The period of gestation is always prolonged when a female is suckling six or more voung In these cases the number of young in the second litter seems to have less influence on the length of the gestation period than has the number of young suckled, but if both litters are very large, the gestation period may be extended to 34 days."

Daniel (1910) in investigations on the mouse, formulated the following law (quoted by King, 1913, as 'Daniel's law'): "The period of gestation, in lactating mothers, varies directly with the number of young suckled."

Both Daniel and King seem to have overlooked the work on the prolongation of gestation in different species of rats by Lataste (1891), in which he states:

"On voit que, d'une facon generate et sauf perturbations accidentelles, le retard de la gestation, dans'une meme espece, est proportionnel au nombre des petits allaites, un nouveau join de retard correspondant a un nourisson de plus."

He proved that the retardation of gestation was due to a delay of the implantation of the ovum during the first 6 to 10 days of pregnancy, due probably to a lack of proper nourishment for the ovum as it enters the uterine cavity. He found that traumatizing the mother early in pregnancy markedly prolonged gestation, while at later periods there was no effect. This is in harmony with my observation that there is very little prolongation of gestation in starvation during the latter half of pregnancy.

Abortion and premature delivery

Although my females were kept in cages with meshed-wire bottoms, so that the products of conception might fall through, no abortions or premature deliveries were observed. Rudolski (1893), in inanition experiments on rabbits and a dog, stated that premature deliveries seldom occurred, and that abortions were never observed Prochownick (1901) cites 48 cases in which women were placed on a restricted diet during the last halt of pregnancy, with no abortions or premature deliveries resulting. He also reviewed the earlier literature upon the subject. Paton (1903) observed no abortions or premature deliveries in guinea-pigs starved during pregnancy. Reeb (1905) observed premature deliveries in 2 rabbits starved from the beginning of pregnancy, but none in rabbits or dogs starved during the last halt of pregnancy.

Although no abortions or premature deliveries were observed, it is interesting to note that 5 of the 12 females that died during pregnancy (table 2) began to bleed from the vagina 1 to 3 days before the end of the normal gestation period. In one of these (B 64), the fetuses had evidently been dead for some time, as upon section and microscopic examination of the swellings in the uterine horns, a degenerating mass of material was found, in which no fetal structures were distinguishable. Rat B 58 (table 2), killed after refeeding 10 days, showed a similar condition in the uterine horns ; but the death of the fetuses evidently occurred earlier, as the swellings of the uterine horns were smaller (5 to 8 mm. in diameter, as compared to 9 to 15 mm. diameter in B 64) .

Macroscopic examination of the placentas of the rats dying after hemorrhage revealed no separation of the placentae and no evidence of beginning labor. Are these cases to be regarded as beginning abortions in which the fetuses have died in utero and therefore analogous to missed abortions occurring in the human? This subject requires further investigation, checked up by careful microscopic examination to determine whether this bleeding is due to a beginning abortion or is the result of degenerative changes in the placenta itself, or perhaps due to changes in the maternal blood.

Sterility

From the total number of 76 females starved during pregnancy (or suspected pregnancy), only 4 became pregnant a second time (B 2, B 29, B 43, and B 44, tables 1,2, and 3) . Of the 76 starved, 21 died, a mortality of 27 per cent. Although the remaining 55 were placed with the males frequently, only 4, or 7 per cent, became pregnant after starvation. Thus it appears that inanition during pregnancy produces a condition of sterility in the majority of the females. Whether this sterility is absolute or only temporary can not be as yet stated, since a sufficient period has not elapsed since the starvation of many of the females.

Jackson and Stewart (1919) likewise found that starvation in young female rats produced sterility in a large number of cases.

Stillbirths and viability of the newborn

From the data in table 1, it is seen that from a total of 129 newborn younofrom mothers starved during pregnancy, 41 were found dead after delivery. Whether these were dead in utero, died during delivery, or afterwards, it is impossible to state. At birth, the newborn dropped through the wire bottom of the cage, and as many were born inclosed within the amniotic sac, death may have resulted from suffocation. The living seemed to be quite vigorous. As they were autopsied as soon as possible after birth, no statements can be made concerning the viability and after-life of these newborn. King (1916), however, has made a study of the growth of albino rats undersized at birth (one a female weighing but 2.6 grams). She states:

"A very small weight at birth indicates that a rat has a handicap in its organization, that environment, however favorable, can not overcome. Such animals, although they appear vigorous and healthy during their growth period and after reaching the adult state, are unquestionably subnormal in regard to the size of the body and the central nervous system."

Size of litters

The average number of young per litter observed in my rats starved during pregnancy was 5.9. King (1915) found an average of 7.0 per litter in 1,089 litters. Apparently starvation during the last half of pregnancy has at least no marked effect on the number of young per litter.

Weight of fetus

Rudolski (1893) starved rabbits and a dog during pregnancy and found that on one-half to one-third of their normal diet the mothers gave birth to healthy, normal offspring and that at times these litters even exceeded in weight those from mothers on a normal diet. However, upon greater reduction (one-fifth to one-thirtieth) of their normal diet, the mothers gave birth to young many of which were dead-born or died soon after birth. The body dimensions were reduced in size. The offspring were toothless and gelatinous in structure, showing a poor development of the subcutaneous tissues and a marked reduction in the amount of fat.

Prochownick (1901), in a report of 48 cases in which women with contracted pelves were placed on a restricted diet during the last months of pregnancy, found the weight of the newborn to be markedly reduced. The average birth-weight was 2,960 and 2,735 grams, respectively, in 24 males and 24 females. Thus, the males were 11 to 14 per cent and the females 14 to 15 per cent below the average weight for that part of Europe (Hamburg). The length, head circumference, and ossification of the cranial bones were not affected. There was, however, a reduction in the amount of subcutaneous fat.

Paton (1903), in a series of female guinea-pigs kept upon a low diet" during pregnancy, found the average weight of the litters to be 28 per cent below that in mothers kept upon a normal diet.

Reeb (1905) obtained a marked reduction in the size of the young in rabbits and a dog placed upon a reduced diet during the last half of pregnancy. Although the pregnant rabbits suffered an average loss of but 7.1 per cent in body-weight during inanition, the individual newborn showed a reduction of 20 to 60 per cent in weight as compared with young from the same mothers on a full diet. The dog lost 8.1 per cent during starvation in pregnancy and the individual young showed a loss of 29 per cent as compared with controls from the same dog on a normal diet.

All the above experiments were carried out by a quantitative reduction in diet. Evvard (1912), however, has shown that undersized young with lessened vigor and vitality result when young pregnant sows (gilts) are fed on corn (maize) alone, in large quantities, but unsupplemented by a diet rich in ash and protein. He attributes this reduction in size and vigor of the offspring chiefly to a lack of calcium salts in a diet of corn alone. Later, Evvard, Dox, and Guernsey (1914) found that normal litters resulted if the corn diet was supplemented by calcium chloride (or calcium carbonate) and blood protein.

Hart, McCollum, Steenbock, and Humphrey ( 1919) fed a diet of corn, grain, and wheat straw to pregnant heifers. The resulting offspring were weak and often dead-born. However, when a suitable salt mixture was added to the above diet, normal calves resulted. Osborne and Mendel (1914) have shown that the maize kernel (corn) is deficient in certain salts and amino acids which are necessary to normal growth (in the rat) .

From my data on the weights of individual rats from mothers starved during the last half of pregnancy, the average gross weight of the newborn is approximately 3 grams. The average gross weight of the normal newborn rat in the same colony has been found to be approximately 5 grams (Stewart, 1918a) , the average in my 10 normal newborn being 4.92 grams. Consequently, underfeeding during the last half of pregnancy apparently causes a reduction of about 40 per cent in the average birth-weight of the newborn albino rat. The gross body-weight of the individual test rats ranged from 2.1 to 4.4 grams. The average percentage loss of weight of the mother during starvation (table 1) was 28 per cent, the loss ranging from 11 to 39 per cent. There is no constant relation between the loss in body-weight of the mother and the size of the newborn or the number in the litter. However, it should be noted that in general the percentage loss of weight was greatest in the heaviest rats which frequently bore the heaviest fetuses. Also, as might be expected, the weight of the newborn tends to be inversely proportional to the loss in the weight of the mother. Thus, the heaviest newborns (4.3 grams) were from a mother losing only 11 per cent in weight.

Just what effect this loss or retardation in birth-weight has upon the relative weights of the various parts, systems, and organs of the newborn rat (or other animals) has not hitherto been ascertained, so far as appears from the available literature. These effects of prenatal starvation, and a comparison of the results obtained in postnatal starvation, will now be considered tor the various organs and parts. In each case the data for the normal newborn will be given first; then the prenatal norm, and finally the condition in the corresponding groups of test rats w'll be compared. This will enable us to see whether, in these stunted test rats with retarded body-weight, the various parts retain their normal proportions, as found in the normal (younger) fetuses of the same body-weight; or, it not, the character and extent of the disproportions which have arisen. Finally, a comparison will be made with the known effects of postnatal inanition.

Relative Weights and Lengths of Body Parts

Ratio of body-weight to body-length. — In the 10 normal newborn rats dissected, the average body length was 51 mm. (net body-weight 4.92 grams) ; Stewart (1918a), using litters from the same colony, found the average body-length to be 50.3 mm. (net body-weight 5.03 grams.)


The ratio of the body-weight (grams) to the body-length (millimeters) in my newborns was 0.096. In Stewart's series (1918a) the ratio is 0.099. The Wistar norm ratio (Donaldson, 1915) is 0.10 tor a 51 mm. rat. In my prenatal fetal controls (table 5), the ratio of the body-weight to the body-length is 0.061 in Group I, and increases through all the groups until in Group V it is 0.092. The ratio for the test rats in Group I is 0.061 and increases through all the groups at nearly the same rate as the prenatal controls to 0.089 in Group V.


By comparing the prenatal and newborn norms, it is found that the smaller the fetus in utero, the smaller is the figure representing the body weight to bodylength ratio; in other words, the younger the fetus (from 2 to 4.1 grams), the less the weight per millimeter of body length. The test rats follow this same law, the ratio being very similar to that in the corresponding normal controls oi the same weight or length. Therefore, it may be stated that the growth ratio, or the relation between fetal body-weight and body-length, is not disturbed by starving the mother during pregnancy.

Ratio of tail-length to body-length. - The ratio J^\^ ™ called the "tail ratio." In my normal newborns the tail ratio ( bod^ength, m"* mm. ) is °- 311 ( sexes combined). Stewart (1918a), in litters from the same colony, found a tail ratio of 0.318 (sexes combined). Jackson (1915a), using litters from both Minnesota and Missouri, found a tail ratio of 0.36 in the newborn (sexes combined). The tail ratio for the prenatal controls in Group I is 0.339 (all females) ; for the test rats, 0.324; for the controls in Group II, 0.288, for the test rats, 0.310; for the controls in Group III, 0.313, for the test rats 0.327; for the controls in Group IV, 0.300, for the test rats, 0.326; for the controls in Group V, 0.296, and for the test rats, 0.323. The tail ratio for the prenatal norm averaged for all five groups is 0.307; for the test rats, 0.322, From these data it is apparent that the ratio of the tail-length to the body-length during the later prenatal growth of the rat (from 2 to 4.1 grams) is about the same as that found at birth; also that inanition in the mother during pregnancy has very slight influence upon the tail ratio of the offspring.


If the absolute data are directly compared, the tail-length in the test rats in all the groups (table 5) is slightly above that of the prenatal norms of the same average body-weight, being 2.8 per cent above in Group 1 and 13.1 per cent on Group V, showing an average gam ol 6 per cent above the norm in all the groups combined. This gain in tail-length, therefore, appears to be less marked in the smaller rats, becoming greater as the size of the body approa ches that normal at birth. It agrees with the observations of Jackson (1915a) and Stewart (1918), that postnatal starvation in growing rats tends to produce relatively long-tailed individuals.

Head

Jackson and Lowrey (1912) give the weight of the head in the newborn albino rat as 1.147 grams, or 21.65 per cent of the body-weight, 5.3 grams (sexes combined) . In my normal newborn series the weight of the head is 1.041 grams, or 21.2 per cent of the body-weight, 4.92 grams.


In my prenatal controls, the average weight of the head forms 24.2, 23.0, 22.7, 21.0, and 20.5 per cent of the body-weight in Groups I, II, III, IV, and V, respectively (computed from table 5). Thus, in the prenatal controls, the head has a higher relative weight in the smaller than in the larger rats, which fact agrees very well with the law formulated by Jackson (1909) : "A relatively large embryonic head is characteristic of vertebrates in general." The head in the smaller prenatal controls also has a higher relative (percentage) weight than in the normal newborns, the elifference decreasing with the increase in the weight of the prenatal controls.


In my test rats the average weight of the head forms 24.0, 24.1, 23.5, 22.3, and 22.0 per cent of the body-weight from Group I to Group V, respectively (computed from table 5) . Therefore, the relative weight of the head is slightly higher in the test rat than in the prenatal controls (except in Group I).

The absolute weight of the head in the test rats exceeds that of the corresponding prenatal controls by 2.8, 6.0, 3.8, 6.5, and 7.6 per cent in groups I, II, III, IV, and V, respectively, averaging 5.3 per cent above in the test rats. Thus in prenatal inanition the head shows a slight increase in weight, which is due partly to the increase in weight of the brain, eyeballs, and the integument covering the head.

In postnatal inanition in young rats, a stronger tendency for the head to increase in weight, even when the body-weight has been held constant, has been noted (table 6). Stewart (1918a) found the head to increase 45 per cent in weight (as compared with controls of the same body-weight) in rats held at a constant bodyweight from birth to 16 days. In a series of rats stunted by underfeeding from birth to 3 weeks (body- weight 10 grams), the average increase in the weight of the head was 16 per cent, as compared with controls of the same body-weight. In rats underfed from age of 3 to 10 weeks, there was an apparent increase in head-weight of 2.1 per cent as compared with controls of the same body-weight (Jackson, 1915a). This slight gain in weight is attributed to the slight gain in skeletal weight, which in the head probably overbalances the loss in weight of the integument.


In both acute and chronic inanition in adult rats, the head increases markedly in relative weight and loses slightly in absolute weight (Jackson, 1915).


From the foregoing it appears that the head manifests its strongest relative growth tendency in rats underfed from birth to 16 days. That this growth tendency, though apparently less intense, is present before birth is evidenced by the increase of the head-weight of the test rats as compared with prenatal controls of the same body-weight.

Extremities and trunk

In my normal newborn series, the fore limbs form 7.0 per cent and the hind limbs 7.6 per cent of the body-weight, 4.92 grams. This is a lower relative weight than given by Jackson and Lowrey (1912) for the relative weight of the extremities in the newborn rat of 5.3 grams, their figures being 7.39 and 9.45 per cent for the fore and hind limbs, respectively. This difference is probably due to a variation in technique. Although the fore and hind limbs were always severed from the body at the shoulder and hip joints, respectively, it was extremely difficult to leave the same amount of skin and muscle attached to the limb in each case.

In my prenatal controls, the fore limbs form 5.3, 6.8, 7.4, 6.7, and 7.1 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus the relative weight of the fore limbs in the smaller prenatal control fetuses is less than in the normal newborn, but this difference (in relative weight) decreases with the increase in the size of the fetus.

In the test rats, the fore limbs form 6.8, 6.8, 7.2, 7.3, and 7.1 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus, with the exception of Group I (in which the relative weight of the fore limbs in the tests quite markedly exceeds that of the prenatal controls) , there is very little difference in the relative weights in the fore limbs of the test rats and prenatal controls, in both of which the fore limbs form a relatively smaller percentage of the body- weight, especially in the smaller rats, than in the normal newborn.

The absolute weight of the fore limbs in the test rats in Group I exceeds that of the prenatal controls by 34 per cent (table 5). In the other groups, however, the difference between the absolute weights of the fore limbs of the test rats and prenatal controls is so irregular that it would be extremely hazardous to draw any conclusions, the average in the test rats being 8 per cent above that of the prenatal controls.

The hind limbs in my prenatal controls form 5.2, 6.3, 6.8, 7.0, and 7.0 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Theretore, as compared with the normal newborn, the hind limbs in the prenatal controls (fetuses) have a lower relative weight, and as in the case of the fore limbs, this difference in relative weight is most marked in the smaller rats (fetuses) and decreases with the increase in size of the prenatal control (fetus).

In my test rats the hind limbs form 6.7, 7.5, 7.4, 7.9, and 7.9 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Therefore, in the test rats, the hind limbs form a higher relative percentage of the body-weight than in the prenatal controls. It thus appears that in the test rats the hind limbs are growing faster than the body as a whole.

The absolute weight of the hind limbs in my test rats exceeds that of the prenatal controls in all the groups, being 36.4, 19.5, 9, 13, and 20 per cent above in ( Groups I, II, III. IV, and V, respectively (table 5), the average being 19.5 per cent.

It is to be noted that in the prenatal controls the hind limbs, as compared with the fore limbs, have a lower or just equal absolute weight, and the earlier in pregnancy the fetus is removed from the mother the larger are the fore limbs as compared with the hind limbs. This is in accord with the law of cranio-caudal progression in growth as formulated by Jackson (1909). This also may explain the larger size of the hind limbs in the test rats, since in the prenatal controls this growth tendency in the hind limbs has not had sufficient time to develop, due to their shorter sojourn in atero, as compared with the test rats, which, although undersized, were born at term.

Jackson and Lowrey (1912), in newborn rats, found the weight of the trunk to be 3.36 grams. In my newborns, the trunk weighs 3.16 grains and forms 64.4 per cent of the average body-weight, 4.92 grams. In my prenatal controls the trunk forms 65.2, 64.0, 63.4, 65.4, and 65.3 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the trunk in the prenatal controls is slighter than in the newborn rats. In my test rats the trunk forms 62.7, 62.3, 62.3, 65.5, and 63.3 per cent of the body-weight in Groups I to V, respectively (computed from table 5).

Thus in the test rat the trunk has about the same relative weight as in the newborn rat, while the relative weight is slightly higher in the prenatal controls corresponding to the smaller size of their heads and extremities. The difference in the size of the trunk, however, is slight, as evidenced by the fact that its absolute weight in the test rats shows an average loss of but 1.6 per cent. This loss of weight in the trunk compensates for the larger head and extremities in the tests.

Consequently it appears that in prenatal retardation by inanition there is a slight increase in the weight of the fore limbs especially in the smaller rats, a more marked increase in the hind limbs, and a slight decrease in the weight of the trunk. In postnatal starvation in young rats held at a constant body-weight there was very little change in the weights of the trunk and extremities as compared with controls of the same body-weight. In general, there was a slight increase in the weight of the head, counterbalanced by a slight decrease in the weight of the trunk and extremities (Jackson, 1915a; Stewart, 1918). During inanition in adult rats, both the head and extremities appear to increase in relative weight, while the trunk decreases (Jackson, 1915; see table 6).

Integument

In my normal newborns the average weight of the integument is 0.794 gram (16.1 per cent of body-weight, 4.92 grams). Stewart (1918a), in newborn litters from the same colony, found the weight of the integument to be 0.754 gram (15 per cent of the body-weight, 5.03 grams). These values are slightly lower than that given by Jackson and Lowrey (1912), which was 0.930 gram (19.8 per cent of body-weight). The difference is probably due to a variation in technique, as it is difficult to remove the skin with uniformity.


In my prenatal controls the weight of the integument forms 11.0, 12.8, 13.4, 13.9, and 14.2 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus it is evident that the weight of the normal integument is relatively less in the fetus, increasing progressively up to birth.

In my test rats the weight of the integument forms 12.4, 13.6, 15.3, 15.3, and 14.5 per cent of the body-weight in Groups I to V, respectively (computed from table 5). The integument in the test rats thus forms a relatively higher percentage of the body-weight (in all the groups) than in the prenatal controls.

The absolute weight (see table 5) of the integument in the test rats exceeds that of the prenatal controls by 18 per cent in Group I, 6.4 per cent in Group II, 14.6 per cent in Group III, 10 pf r cent in Group IV, and 3 per cent in Group V. The average increase in all the groups is 10.4 per cent. Although this increase in weight is irregular, it has a downward trend from Group I to Group V and shows that the nearer the prenatal controls and test rats approach their normal birth-weight, the less is the difference in the relative (percentage) and absolute weights ol their integuments. This increase may be due to the longer interval the test rats remained in utero as compared with the prenatal controls, or to the fact that the skin has a stronger growth tendency at this time as compared with some of the other parts of the body. It is interesting to note (see table 6) that Stewart (1918) found the integument to remain at a constant weight in rats starved from birth to 3 weeks of age, while in older rats starved for longer or shorter periods the loss in weight of the integument was quite marked. In a younger series kept at a maintenance diet from birth to 11 to 22 days, Stewart (1918a) found the absolute weight of the integument in the test rats to be 25 per cent above that in the controls of the same body-weight. Jackson (1915) found the integument to lose weight in nearly the same proportion as the whole body in acute and chronic inanition in adult rats.

Skeleton

As explained under the section on materials and methods, my "moist" skeleton probably corresponds closely to thatreferred to by Jackson (1915a) as the cartilaginous skeleton. Since the "gold dust" solution used to rid the skeleton of its ligaments and periosteum acted too strongly upon the skeleton in my very small rats, causing a disintegration of the cartilages, no attempts were made to obtain anything corresponding to the cartilaginous skeleton. My observations on the "dried skeleton" are consequently on the dried ligamentous skeleton. Jackson and Lowrey (1912) obtained a value of 0.810 gram tor the ligamentous skeleton in the newborn rats, while in my normal newborn the "moist" skeleton weighs but 0.381 gram, 7.8 per cent of body-weight, 4.92 grams. However, this agrees very well with the weight of the newborn moist skeleton of 0.377 gram or 9.0 per cent body-weight— 4.92 grams— given by Conrow (1915). It must be stated, however, that despite the greatest care taken in cleaning the skeletons, their range of weight was very great, even in rats of equal weights (see table 5).

In my prenatal controls, the weight of the moist skeleton forms 7.2, 7.2, 7.4, 7.1, and 6.7 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus the moist skeleton in the prenatal controls has a relative weight slightly below that of the normal newborn rat.

In my test rats the weight oi the moist skeleton forms 5.0, 7.0, 7.4, 7.2, and 7.0 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus there is very little difference in the relative weight of the moist skeleton in the test rats and prenatal controls, except in Group I, where its relative weight in the test rats is considerably below that of the prenatal controls. This difference is probably due to errors in technique.

By comparing the absolute weights of the moist skeleton in the test rats with the prenatal controls in table 5, it will be seen that hi Group I the absolute weight of the moist skeleton in the test rats is 27 per cent less than in the prenatal controls of the same body-weight. Since such a marked difference can not be accounted for by any change in body-length (in fact, the average body-length of the test rats is 7.3 per cent greater than in the prenatal controls of this group) , it must be attributed to errors in technique. In the other four groups the difference in the absolute weights of the moist skeleton in the test rats and prenatal controls is very slight and wholly within the limits of error, considering the difficulties of technique. Probably there is very little real difference between the absolute weight of the moist skeleton in test rats and prenatal controls, but one can hardly reach any definite conclusion.


It should be noted, however, that in postnatal inanition the skeleton (undried) shows its greatest increase in weight, 32 per cent, in rats underfed from the age of 3 weeks to 1 year (Stewart, 1918). In rats underfed from birth to 16 days the gain in the skeleton (with musculature) is but 6 per cent (Stewart, 1918a). This seems to show that the growth tendency in the skeleton is relatively weak at birth, which may explain its apparent loss of weight in my test rats.


In my normal newborn series the weight of the dried skeleton is 0.089 gram or 1.8 per cent of the body-weight, 4.92 grams. Conrow (1915) found the dried skeleton to be 1.9 per cent of the body-weight in the normal newborn rat (bodyweight, 4.2 grams; calculated weight of dried skeleton, 0.081 gram).


In my prenatal controls the weight of the dried skeleton forms 1.4, 1.5, 1.5, 1.7, and 1.6 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the dried skeleton in the prenatal control has a relative weight slightly below that of the normal newborn rat.


In my test rats the weight of the dried skeleton forms 1.5, 1.8, 1.7, 1.8, and 1.7 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus the relative weight of the dried skeleton in the test rats is slightly higher than in the prenatal controls.


Concerning the absolute weight of the dried skeleton, however (see table 5), the results obtained are different from those in the case of the moist skeleton. Although in Groups I, II, and III (see table 5) the absolute weights of the moist skeletons in the test rats were 27, 1.8, and 5.0 per cent below the prenatal controls of the respective groups, and 0.4 and 0.01 per cent above in groups IV and V, respectively, the absolute weight for the dried skeleton of the test rats exceeds that of the prenatal controls in all five groups, the excess being 7, 20, 14, 9, and 9 per cent, respectively, from Group I to V (see table 5), averaging 12 per cent above for all groups.


This increase in the weight of the dried skeleton in the test rats is evidently due to an increase of dry substance in the bones, cartilages, and ligaments. Therefore, since the dry skeleton shows a relatively greater increase in the test rats as compared with the prenatal controls of the same body-weight, it is apparent that, although the body-weight is retarded, the relative percentages of solid substance and water in the test rats tend to approach that found in the normal newborn rat. The tendency of the skeleton to grow in mass (although at a retarded rate) in cases of underfeeding in rats was observed by Jackson (1915a) and by Stewart (1918). Lowrey (1913) found that in the postnatal growth of the rat the amount of dry substance in the ligamentous skeleton increases with age, being 18.1 per cent at birth, 33.3 per cent at 20 days, 39.2 per cent at 6 weeks, 45.9 per cent at 10 weeks, 50.4 per cent at 5 months, and 52.6 per cent at 1 year.


No observations were made on any of the skeletons to determine whether there was any variation in the normal process of differentiation (developmental changes) between tha test rats and prenatal controls. Jackson (1915a) and Stewart (1918), however, found that during maintenance of body-weight by underfeeding in youngrats, skeletal growth and differentiation occurred apparently in a normal manner, although at a retarded rate.


Musculature

The musculature was not weighed separately, but was weighed together with the skeleton and its weight obtained by subtracting the latter from the combined weight. The weight given by Jackson and Lowrey (1912) for the newborn rat is 1.15 grams or 24 per cent of body-weight, 5.3 grams; while in my newborns the weight of the musculature was 1 .77 grams or 36 per cent of the body-weight, 4.92 grams. This marked difference is probably due to a variation in technique, as in all my rats the fat was included with the musculature. The reason for this difference in technique is obvious, because in the small rats the fat was poorly differentiated from the muscle.

In my prenatal controls the musculature forms 28, 32, 32, 36.5, and 37.5 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus in the prenatal controls it is evident that the relative weight of the musculature is less in the smaller rats, increasing progressively up to birth.

In my test rats the musculature forms 28, 30, 31, 33, and 34 per cent of the body-weight in Groups I toV, respectively (computed from table 5). Thus, in both the test rats and prenatal controls there is apparently an increasing tendency for the musculature to make up a larger proportion of the body-weight as the rat increases in size; that is, the muscle is growing at a relatively faster rate than the remainder of the body, the increase being slightly more marked in the prenatal controls than in the test rats.

The absolute weight of the musculature in the test rats is slightly below that of the prenatal controls with the exception of Group I (see table 5), in which its absolute weight in the test rats is 7 per cent above that in the prenatal controls. Taking the groups as o whole, the absolute weight of the musculature in the test rats is but 5 per cent below that in the prenatal controls. This difference is slight, and may in part be due to a decrease in the fat in the test rats. On account of the difficulties encountered in separating the fat from the musculature, they were weighed together, as previously stated.

In postnatal inanition in young rats, there is apparently a slight gain in weight of the musculature. It shows an increase of but 6, 8, 10, and 3 per cent, respectively, in rats underfed from birth to 16 days, from birth to 3 weeks, from birth to 10 weeks, and from 3 to 10 weeks of age (Stewart, 1918, 1918«; Jackson, 1915a) . The greatest gain observed (25 per cent) was in rats underfed from 10 weeks to 8 months of age (Jackson, 1915a). In both acute and chronic inanition in adult rats the musculature loses in about the same proportion as the body as a whole (Jackson, 1915).

In general, it appears that the musculature manifests a relatively weak growth tendency during both prenatal and postnatal inanition, with even a slight loss in the former.

Visceral group

The visceral group includes the brain, spinal cord, eyeballs, and thyroid, as well as the abdominal and thoracic viscera. Jackson and Lowrey (1912) give the weight of the visceral group in the newborn as 0.954 gram, or 18 per cent of the body-weight, 5.3 grams. Stewart (1918a) gives the visceral group a weight of 0.871 gram, or 17.3 per cent of the body-weight, 5.03 grams. The visceral group in my normal newborn series weighs 0.817 gram, or 16.6 per cent of the bodyweight, 4.92 grams.

In my prenatal controls the weight of the visceral group forms 23, 21 , 18.5, 19.5, and 19 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Therefore it is evident that the relative weight of the visceral group in the prenatal controls (fetuses) exceeds that of the normal newborn rat. This difference is most marked in the smaller rats (fetuses), decreasing as the birth-weight is approached, showing that in the fetal life of the rat (from 2 to 4.1 grams) the viscera constitute a larger proportion of the body-weight than at birth.

In my test rats the weight of the visceral group forms 16.2, 16.6, 16.6, 16.2, and 15.2 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus, in the test rats the visceral group forms a slightly smaller percentage of the body-weight than in the normal newborn, while in the prenatal controls the converse is true. The relative weight of the visceral group is markedly lower in the test rats than in the prenatal controls.

In my test rats the absolute weight of the visceral group is less than that of the prenatal controls in all the groups (table 5) . In Groups I to V the absolute weight of the visceral group in the test rats is 27, 21, 7, 17, and 20 per cent below that of the prenatal controls in the corresponding groups, averaging 18.4 per cent below.

Thus in prenatal inanition the visceral group shows a marked retardation in growth. This is due chiefly to the retarded growth of the liver and lungs.

These results are directly opposed to those in postnatal inanition shortly after birth. Stewart (1918, 1918a) found that the absolute weight of the visceral group exceeded that of controls of the same body by 46, 28, and 38 per cent in rats underfed from birth to an average of 16 days, from birth to 3 weeks of age, and from birth to 10 weeks of age, respectively (table 6). In rats underfed from the age of 3 weeks to 10 weeks and from the age of 3 weeks to 1 year, there was no marked change in the weight of the visceral group (Jackson, 1915a; Stewart, 1918); while in rats underfed from 10 weeks of age to 8 months, Jackson (1915a) found the weight of the visceral group to be 12 per cent below the normal. He found that the visceral group as a whole undergoes very little change in relative weight in adult rats during either acute or chronic inanition.

From the foregoing data it is evident that the growth tendency of the visceral group in the rat during inanition is relatively weak before birth, strongest shortly after birth, and decreases gradually thereafter.

Remainder

The "remainder" is obtained by subtracting the weight of the integument, "moist" skeleton, musculature, and viscera from the net body-weight. It thus includes the loss by evaporation of fluids which escape from the body during dissection, also the larynx, trachea, esophagus, salivary and lymph glands, large vessels, and pieces of fat in the omentum. The remainder may vary with the amount of fat removed from different portions of the body.


In general, no attempt was made to remove any of the fat, such as the "nuchal fat pad," retroperitoneal fat, etc., all of which was included in the musculature.

In my normal newborns (body-weight 4.92 grams) the average weight of the remainder was 1.05 grams (21 per cent of body-weight); Stewart (1918a) found its weight to be 1 .52 grams (30 per cent of net body-weight, 5.03 grams) . This weight is considerably higher than mine, probably due to the fact that he included more fat with the remainder than with the musculature. Jackson and Lowrey (1912) , however, found its weight to be 0.97 gram (20.56 per cent of body-weight, 5.3 grams), a value very close to mine.

In my prenatal controls the weight of the remainder forms 31, 27, 28, 23, and 23 per cent of the body- weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the remainder in the smaller prenatal control rats (fetuses) markedly exceeds that of the normal newborn rat, the difference decreasing as the normal birth-weight is approached.

In my test rats the weight of the remainder forms 37, 34, 31, 28, and 30 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Therefore the relative weight of the remainder in the test rats exceeds that of the prenatal controls in all the groups.

The absolute weight of the remainder in my test rats was considerably above that of my prenatal controls in all the groups, the average being 25.4 per cent above (see table 5) .

This relative and absolute increase in the remainder is directly opposed to the results obtained in investigations on postnatal starvation (see table 6) . In rats held at a constant weight from birth to 16 days, in another group underfed from birth to 3 weeks (body-weight 10 grams), and in another series underfed from birth to 10 weeks, Stewart (1918a, 1918) found in the remainder a decrease of 59, 40, and 23 per cent, respectively, as compared with normal controls of the same body- weight. In rats underfed from the age of 3 to 10 weeks, however, Jackson (1915a) found but 2 per cent decrease in the remainder. In young rats underfed up to 1 year of age he found a decrease of but 5 per cent, while in Stewart's series (1918) there is a decrease of 33 per cent. In acute and chronic inanition in adult rats there is a definite decrease in the weight of the remainder, probably due to a loss of fat (Jackson, 1915).

Why the remainder should decrease during postnatal starvation and increase during prenatal inanition is difficult to explain. Possibly there is a larger amount df circulating fluids (blood, lymph, etc.) in my test rats than in the prenatal controls. This increase in the remainder evidently compensates for the loss in weight of the visceral group. This is the converse of what occurs in postnatal starvation, as found 1 y Stewart (1918a) in the rats held at birth-weight.

Brain

In my normal newborns the average weight of the brain is 0.235 gram (4.8 per cent of the body-weight, 4.92 grams) . Stewart (1918a) gives the weight of the brain in the newborn as 0.224 gram (4.5 per cent of the body-weight, 5.03 grams). Jackson (1913) found the weight of the brain in the newborn rat to be 4.8 per cent of the gross body-weight.


In my prenatal controls the weight of the brain forms 6.2, 5.6, 5.0, 4.8, and 4.4 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus in the prenatal controls the relative weight of the brain in the smaller rats (fetuses) is greater than that of the normal newborn, this difference in relative weight decreasing, however, as the birth-weight is approached.

In my test rats the weight of the brain forms 6.6, 6.2, 5.6, 5.3, and 5.0 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus, in the test rats the brain forms a slightly higher per cent of the body-weight than in the prenatal controls; in both, the smaller the rat, the greater is the weight of the brain relative to the body-weight. Since in the test rats, especially in the smaller ones, the brain tends to form a relatively larger part of the body-weight than in either the normal newborns or in the prenatal controls, it may be quite safely assumed that in a state of inanition of the mother the brain of the fetus has a greater growth tendency than does the remainder of the body as a whole.

In the test rats the absolute weight of the brain exceeds by 12 to 13 per cent (average 12.5 per cent) that in the corresponding prenatal norms, constantly throughout all the groups (see table 5) .

Comparing these results with those obtained in postnatal inanition by Jackson and Stewart (see table 6), it is seen that the brain shows its greatest tendency to increase in weight in rats underfed from birth to 16 days (Stewart, 1918a). Here the brain shows a gain of 125 per cent in absolute weight above controls of the same body-weight. This gain drops to 60 per cent in rats (body-weight 10 grams) underfed from birth to 3 weeks (Stewart, 1918) ; and in rats starved from birth to 10 weeks the gain is but 8 per cent. In rats underfed from 3 weeks after birth to 10 weeks of age the brain shows little or no change (Jackson, 1915a).

Hatai (1904) found a decrease of 5 per cent in the absolute weight of the brain in young rats losing 30 per cent of their body-weight on an unfavorable diet of starch and beef fat. Later (1908) he found no change in the brain-weight in rats stunted on an unfavorable diet, as compared with normal rats of the same bodyweight.

Donaldson (1911), in young rats held at maintenance from 30 to 51 days ol age, found the brain-weight to average 7 per cent less than in normal controls of the same age. If a comparison is made, however, with the calculated initial brainweight, as he points out, the average weight of the brain is 3.6 per cent greater in the underfed rats.

In adult rats, during both acute and chronic inanition, Jackson (1915) observed that the brain even loses slightly in weight.

From the foregoing results, it may be assumed that in the rat during inanition the brain possesses its strongest growth tendency at birth and that this tendency decreases with age (see table 6) . Whether this growth impulse is stronger or weaker before birth is hard to decide. From a comparison of the data it would seem to be weaker before birth, since in my test rats from underfed mothers the weight of

the absolute brain increased but 12.5 per cent above that of the prenatal norms, while Stewart (1918a), in starvation 17 to 22 days after birth, found the absolute weight of the brain to gain 125 per cent above that of the controls of the same body-weight. It must be remarked, however, that in my tests the exact character and extent of the inanition of the fetus are somewhat uncertain.

Spinal cord

In my normal newborns the spinal cord weighs 0.036 gram (0.71 per cent of the body-weight, 4.92 grams). Stewart (1918a) gives the weight of the spinal cord in the newborn as 0.035 gram (0.70 per cent of the body-weight, 5.0 grams) . The Wistar norm (Donaldson, 1915) for the spinal-cord weight is 0.034 gram at body-weight of 4.95 grams.

The weight of the spinal cord in my prenatal controls forms 1.12, 1.00, 0.91, 0.83, and 0.75 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus it is evident that the spinal cord, similar to the brain, in the prenatal controls has a higher relative weight than in the normal newborn rat.

In my test rats the weight of the spinal cord forms 1.13, 1.01, 0.86, 0.80, and 0.75 per cent of the body-weight in Groups I to V, respectively (computed from table 5).

Thus, in the smaller rats, both the test rats and prenatal controls, as compared to the normal newborns, the spinal cord torms a relatively higher percentage of the body-weight, this tendency lessening with the increase in size of the rats, until in the larger rats this difference in relative weight disappears.

From the data in table 5, the absolute weight of the spinal cord is lower in the test rats than in the prenatal controls, with the exception of Groups I and II, where it is respectively 6 and 2 per cent higher in the test rats. The absolute weight in all the groups averages but 0.26 per cent higher in the prenatal controls than in the test rats. This is such a slight difference that it might very well be attributed to errors in technique, since it is very difficult to remove the cord intact from these small rats and also to sever the head from the trunk at exactly the same place. Probably there is very little change in the spinal cord of the fetus during inanition in the mother. The fact that the body-length in the tests and controls varies but little (1 per cent higher in the test rats) would lead one to expect but little difference in the corresponding weights of the spinal cord.

The results obtained in postnatal inanition, however, might lead one to expect an increase in the size of the cord in the stunted individual. Bechterew (1895), in acute inanition of puppies and kittens, made a study of the central nervous system after death of the animal and found the least loss in the spinal cord. Donaldson (1911) found a slight increase in the weight of the spinal cord in young rats, held at body-weight of 34 grams from 30 to 51 days of age. Jackson (1915) found no change in the weight of the spinal cord in acute inanition in adult rats, while in chronic inanition in adult rats he found a slight decrease in the weight.

In newborn rats, however, Stewart (1918a) noted a marked tendency tor the cord to continue growing during inanition in which the body is kept at nearly constant weight. From the data in table 6, it is evident in underfed young rats that the spinal cord possesses a very strong growth tendency, greatest at or shortly after birth, but also present up to adult life. It should be noted that this growth tendency persists for a longer time in the cord than in the brain, probably due to the fact that the brain normally completes its postnatal growth at a relatively earlier age than does the cord.

Why the cord should lose while the brain gains in weight during fetal inanition is difficult to explain. So far as their normal growth tendency during the fetal period is concerned, both appear to be decreasing in about the same relative proportion, judging from a comparison of their prenatal growth norms.

Eyeballs

The eyeballs in my normal newborns weigh 0.025 gram and form 0.50 per cent of the body-weight, 4.92 grams. In Stewart's (1918a) newborn they weighed 0.0235 gram and formed 0.47 per cent of the body- weight, 5.03 grams. Jackson (1913) gives the weight of the eyeballs in the newborn as 0.025 gram and 0.53 per cent of the body-weight.

In my prenatal controls the eyeballs form 0.38, 0.42, 0.42, 0.38, and 0.37 per cent of the body- weight in Groups I to V, respectively (computed from table 5) . Compared with the normal newborn rat, the relative weight of the eyeballs is much lower in the prenatal controls.

In my test rats the eyeballs form 0.57, 0.52, 0.50, 0.48, and 0.46 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus it is evident that the eyeballs in the test rats have a much higher relative weight than in the prenatal controls. In the test rats the relative weight of the eyeballs is about the same as that of the normal newborn. (In the smaller rats it is slightly higher.)

The absolute weight of the eyeballs is markedly higher in the test rats than in the controls in all the groups (table 5), being most pronounced in Group I (the smallest rats), in which the average absolute weight of the eyeballs of the test rats is 56 per cent above that in the prenatal controls. It is interesting to not( that, in the range of their weights, in Group I the heaviest eyeballs in the prenatal control just equal the lightest in the test rats. In the other groups the eyeballs in the test rats show an increase in absolute weight above the prenatal controls of over 20 per cent. The average total excess of the absolute weight of the eyeballs in the test rats above that in the prenatal controls is 31.4 per cent.

These results are quite in accord with those obtained in postnatal inanition, although less marked. In postnatal inanition the strongest growth capacity of the eyeball is exhibited in newborns underfed from birth to an average of 16 days (Stewart, 1918a), the increase being 146 per cent (table 6). This growth capacity of the eyeball during inanition then decreases somewhat, but rises again in older rats and persists in animals underfed up to 1 year of age. In older rats (adults), in both acute and chronic inanition, the eyeballs lose slightly in weight according to Jackson (1915). He suggests that this remarkable capacity of the eyeball to continue its growth during inanition may be due to its power to absorb water, which makes up so large a proportion of its composition.

Thymus

In my normal newborns, the average weight of the thymus is 0.0070 gram or 0.14 per cent of the body-weight, 4.92 grams. Stewart (1918a) gives the weight of the thymus in the newborn as 0.0079 gram or 0.15 per cent of the bodyweight — 5.03 grams. The Wistar norm (Donaldson, 1915) is 0.00S0 gram, bodyweight, 4.9 grams.

In my prenatal controls the thymus forms 0.11, 0.13, 0.13, 0.13, and 0.12 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus the relative weight of the thymus in the prenatal controls is slightly lower than in the normal newborn rat.

In my test rats the thymus forms 0.08, 0.09, 0.11, 0.11, and 0.10 per cent of the body weight in Groups I to V, respectively (computed from table 5). Thus the thymus forms a much smaller part of the body-weight in the test rats than in the prenatal controls; that is, its growth has been retarded in the test rats. This is more clearly brought out by a comparison of the absolute weights. In Group I the absolute weight of

the thymus, in the test rats, is 29 per cent below that of the prenatal controls; in Group II, 33 per cent below; in Group III, 12 per cent below; in Group IV, 16 per cent below; and in Group V, 15 per cent below, averaging 21 per cent below for all groups. Thus it is seen that the growth of the thymus is considerably retarded in the rat fetus during inanition of the mother.

These results also agree with the loss of weight (hunger involution) of the thymus in cases of postnatal inanition. Jonson (1909), in young rabbits, kept a constant body-weight by underfeeding for 4 weeks, found the weight of the thymus to be reduced to one-thirtieth of that in the controls, the greatest loss of weight being in the cortex. He also found that the reduction in weight of the thymus was proportionate to the loss of the body-fat. This reduction in weight of the thymus in rabbits is much more marked than that obtained by Jackson and Stewart upon rats. Jackson (1915a) found a loss of 90 per cent in the thymus in young rats held at maintenance from the age of 3 to 10 weeks and also in young rats underfed 10 weeks to 8 months. Stewart (1918 and 1918a) found losses of 80, 30, and 49 per cent, respectively, in the weights of the thymus in young rats underfed from birth to 10 weeks, from birth to 3 weeks, and held at birth-weight for 16 days. Jackson (1915) found no marked change in the weight of the thymus in cases of acute and chronic inanition in adult rats, at which age involution of the thymus had already occurred. The thymus normally reaches its maximum absolute weight in the rat at 85 days (Hatai, 1914) and at 1 year it has undergone a complete age involution (Jackson, 1913).

Heart

In my normal newborns, the average weight of the heart is 0.027 gram or 0.55 per cent of the body-weight, 4.92 grams. Jackson (1913) gives its weight in the newborn as 0.030 gram, or 0.65 per cent of the body-weight, 5.08 grams. Stewart (1918a) gives a weight of 0.031 gram, or 0.61 per cent of the body-weight, 5.03 grams.


In my prenatal controls the weight of the heart forms 0.49, 0.52, 0.49, 0.50, and 0.44 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the heart in the prenatal controls is considerably less than in the normal newborn rat.


In my test rats the weight of the heart forms 0.55, 0.53, 0.54, 0.53, and 0.49 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the heart in the test rats is slightly higher than in the prenatal controls. The relative weight in both the test rats and prenatal controls is less than that in the normal newborn rats. It is also evident that in both the prenatal controls and test rats the relative weight of the heart is greater in the smaller as compared with the larger rats.

The absolute weight of the heart is constantly higher in the test rats than in the prenatal controls, the difference being most marked in Group I (table 5) in which the heart weight in the test is 17 per cent higher than that in the prenatal controls. This difference, however, is not so pronounced in the other groups, averaging for all groups 8 per cent above in the test rats.

This gain in heart-weight in prenatal starvation agrees with the results of Stewart (1918a), who noted a gain of 26 per cent in absolute weight of the heart in test rats kept at a birth-weight of about 5 grams for an average ol 16 days. However, in another series (Stewart, 1918) starved from birth to 3 weeks (body-weight 10 grams), the heart showed a loss of 5 per cent. In still another group, underfed from birth to 10 weeks (body-weight 24 grams), Stewart (1918) found a gain of 27 per cent in the weight of the heart. In slightly older rats, underfed for various periods, the heart loses slightly (Jackson, 1915a; Stewart, 1918), while in adult rats the heart shows a decided loss in both acute and chronic inanition (Jackson, 1915).

Lungs

Jackson (1913) gives the absolute weight of the lungs as 0.078 gram or 1.6 per cent of the body-weight, 5.1 grams. The Wistar norm (Donaldson, 1915) is 0.079 gram, or 1.6 per cent of the body-weight, 4.9 grams. In my newborn controls the weight of the lungs is 0.073 gram, or 1.5 per cent of the body- weight) , 4.92 grams.

In my prenatal controls the lungs form 2.8, 2.7, 2.3, 2.0, and 2.1 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the lungs is markedly higher in the prenatal controls than in the normal newborn rats. This difference in relative weight is greatest in the smaller rats and decreases as the birth-weight is approached.

In my test rats the lungs form 1.2, 1.5, 1.4, 1.5, and 1.3 per cent of the bodyweight in Groups I to V, respectively (computed from table 5) . Thus, in the test rats the lungs have a relative weight which is about that of the normal newborn rat, whereas in the prenatal controls the relative weight is approximately double that at birth.

The absolute weight of the lungs in the test rats is 54, 44, 40, 23, and 36 per cent below that of the prenatal controls in Groups I to V, respectively, averaging 39.4 below for all groups. It is interesting to note that in the range of the individual weights the largest lungs in the test rats about equal in size the smallest in the controls.

This lack of ability of the lungs to grow, manifested by a subnormal weight during prenatal inanition, agrees with the results obtained in the postnatal starvation experiments (table 6). Stewart (1918a) found a slight gain (3 per cent) in the lungs of rots underfed from birth to an average of 16 days. On underfeeding from birth to 3 weeks, and from birth to 10 weeks of age, the lungs showed a loss of 26 per cent in both series (Stewart, 1918). Jackson (1915a) found that the lungs lose 15 per cent in rats starved from the age of 3 weeks to 10 weeks. He also found a loss of 13 per cent in the lungs in a group underfed between the ages ol 10 weeks and 8 months. Stewart (1918), however, found the lungs in rats underfed from an age of 3 weeks to 1 year to gain in weight 28 per cent (probably pathological). Jackson (1915) found that the lungs show a tendency to lose weight in adult rats in both acute and chronic inanition and that this loss of weight is about in proportion to the loss of the body as a whole. Consequently, it may be concluded that the lungs exhibit a very weak growth tendency during prenatal as well as during postnatal conditions of inanition.

Liver

The Wistar norm (Donaldson, 1915) for the liver of the newborn rat is 0.205 gram, with a body-weight of 4.9 grams. Stewart (1918a) gives the weight as 0.245 gram or 4.9 per cent of the body-weight, 5.03 grams. Jackson (1913) finds a weight of 0.230 gram or 4.3 per cent of the body weight. In my newborns the weight of the liver is 0.250 gram or 5.1 per cent of the body-weight, 4.92 grams.

In my prenatal controls the liver forms 9.1, 8.7, 7.8, 8.1, and 7.7 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the liver in the prenatal controls markedly exceeds that of the normal newborn rat. This difference in relative weight decreases, however, as the normal birth-weight is approached.

In my test rats the liver forms 4.1, 4.5, 4.6, 4.9, and 4.4 per cent of the bodyweight in Groups I to V, respectively (computed from table 5) . In the smaller test rats, the liver forms a relatively smaller percentage of the body-weight than in the normal newborns. In the prenantal controls, however, the liver forms a much higher relative percentage of the body-weight than in either the normal newborns or in the test rats.


In the test rats the absolute weight of the liver is markedly subnormal in all the groups (table 5), averaging 45 per cent below that of the prenatal controls. In the range of the individual weights in the same groups the highest weight for the liver in the test rats is much below the lowest weight in the prenatal control. Thus in prenatal inanition the growth of the liver is markedly retarded, reaching an absolute weight of approximately one-half that of the prenatal controls.


In postnatal inanition, Stewart (1918a) found that the liver loses 23 per cent in rats held at a constant weight from birth to an average of 16 days (table 6). In two other groups underfed from birth to 3 weeks, and from birth to 10 weeks, he found that the liver gains in weight 17 and 64 per cent, respectively. Jackson ( 1915a), in young rats underfed from the age of 3 weeks to 10 weeks, found a gain of 10 per cent in the liver-weight. In rats starved for a longer period, or where it was begun later, the liver shows a loss of weight (Jackson, 1915a; Stewart, 1918). Jackson (1915) found that the liver loses markedly in cases of acute and chronic inanition in adult rats.


Thus it would seem that in prenatal life and for a period up to several days after birth, the liver during inanition has a very weak growth tendency, which becomes stronger after the first week of postnatal life and persists up to 6 weeks or 2 months of age, then decreases until it is very weak again as the adult stage is approached.

Spleen

The Wistar norm (Donaldson, 1915) for the spleen in the newborn rat is 0.00S for a body-weight of 4.9 grams. Jackson (1913) gives the weight of the spleen as 0.010 gram, or 0.22 per cent of the body-weight. Stewart (1918a) finds the weight to be 0.01 1 gram, or 0.22 per cent of the body-weight, 5.03 grams. In my normal newborns the average weight of the spleen is 0.010 gram, or 0.20 per cent of the body-weight, 4.92 grams.

The spleen in the prenatal controls forms 0.08, 0.08, 0.13, 0.14, and 0.15 per cent of the body-weight in Groups I to V, respectively, while in the test rats in the corresponding groups it forms 0.12, 0.12, 0.16, 0.17, and 0.21 per cent of the bodyweight (computed from table 5). Thus the spleen in the prenatal controls forms a much smaller proportion of the body-weight than it does in the normal newborn; that is, in the rat fetus the spleen is at first relatively small (0.08 per cent of bodyweight in a 2.19-gram fetus), but gradually increases in size up to shortly before birth (0.15 per cent of the body-weight in a 4.19-gram fetus), when, in order to reach its normal relative percentage of the newborn body- weight, it must increase rapidly in size (an increase from 0.15 to 0.22 per cent of the body-weight while the fetus is growing from 4.19 to 5.0 grams).

Jackson (1909) in referring to the human fetus says:

"The spleen is at first relatively small, but increases slowly to an average of 0.176 per cent of the whole body in the seventh month. About this time it appears to increase rapidly in relative size, averaging over 0.4 per cent in the eighth and ninth months. In the full-term still-born (143 cases) the spleen averages 0.32 per cent of the total body weight , and in the live-born (101 cases) 0.43 per cent."

Lowrey (1911) finds practically the same course of growth in the spleen of the pig fetus.

Thus it appears that the prenatal growth of the spleen in the rat is similar to that observed in the human and the pig. In all three animals the spleen apparently develops a strong growth tendency shortly before birth. This probably explains the increase in the relative weight of the spleen in the test rats. Since the test rats have a longer time in the uterus, this late growth tendency in the spleen has more opportunity to develop than in the prenatal controls.

The absolute weight of the spleen in the test rats is constantly higher than that in the prenatal controls in all the groups (see table 5), averaging 34 per cent above.

This growth of the spleen during prenatal inanition agrees very well with the results obtained during postnatal starvation. Stewart (1918a) found the spleen to gain 38 per cent in rats kept at birth-weight for an average of 16 days of age. In another series (Stewart, 1918) underfed from birth to 3 weeks of age, the spleen lost 49 per cent. In a third series, starved from birth to 10 weeks of age, the spleen gained 24 per cent. Jackson (1915a) found the spleen to lose 42 per cent in rats starved from 3 weeks of age to 10 weeks. In two series starved during later periods (Jackson, 1915a; Stewart, 1918) there was no material change in its weight.


In adult rats in chronic inanition the reduction in the weight of the spleen is about the same as that for the whole body, while in acute inanition the loss is much greater (Jackson, 1915).


Intestines

The intestines, with their contents, have an average weight of 0.141 gram and form 3.0 per cent of the body-weight (4.92 grams) in my normal newborns. The empty intestines have an average weight of 0.062 gram or 1.3 per cent of the body-weight.

In my prenatal controls the intestines with contents form 1.6, 1.9, 1.9, 2.4. and 2.3 per cent of the body-weight (computed from table 5) . Thus the relative weight of the intestines with contents is considerably less in the prenatal controls than in the normal newborn rat, the difference decreasing, however, as the prenatal control fetuses approach their birth- weight.

In my test rats the intestines with contents form 1.8, 2.2, 2.5, 2.4, and 2.4 per cent of the body-weight in Groups I to V, respectively (computed from table 5.)

Thus the relative weight of the intestines with contents is slightly higher in the test rats than in the prenatal controls.

The empty intestines in my prenatal controls form 0.64, 0.75, 0.76, 0.93, and 1.60 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus it is evident that the relative weight of the empty intestines is lower in the fetus, increasing progressively up to birth.

In my test rats the empty intestines form 0.60, 0.71, 0.95, 0.82, and 0.90 per cent of the body-weight in Groups I to V, respectively (computed from table 5).

Therefore the relative weight of the empty intestines in the test rats is slightly less than that of the prenatal controls.

The absolute weight of the intestines with contents, in the test rats, exceeds that of the prenatal controls in Group I, II, III, and V by 24, 17, 31, and 2 per cent, respectively. In Group IV the absolute weight is 0.06 per cent lower in the test rats. From the foregoing it is evident that the intestinal contents in the smaller test rats markedly exceeds that of the smaller prenatal controls (fetuses), this difference disappearing in the larger rats, i. e., as the normal birth-weight is approached.

The absolute weight of the empty intestines, however, in the test rats of Group I and II is below that of the prenatal controls, 3 and 5 per cent, respectively. In Group III in the test rats it is 27 per cent above, and in Groups IV and V it is 12 and 16 per cent respectively below that of the controls ; averaging 2 per cent below in the test rats for all groups. This difference in absolute weight is slight and may be due to the difficulty of removing the intestinal contents in a uniform manner. It is difficult to explain on any other premises why the absolute weight of the intestines with contents in the test rats should exceed that of the controls by 15 per cent while below them 2 per cent in absolute weight when empty. Jackson (1915a), however, in underfed young rats, found an increase in the intestinal contents, while the empty intestines lost in weight. Since the full stomach in my test rats weighs 3.7 per cent less than that of the prenatal controls, there may be a passage of stomach contents into the intestines, with a possible increase of meconium and mucus in the older rats (test), which may account for the increase in the absolute weight of the full intestines in the test rats.

There may be a retardation of the growth of the intestines during prenatal inanition while the stomach increases slightly in weight. However, on account of the irregularities of the results obtained, it would be hazardous to venture any definite conclusion.

It has been found, however, that in postnatal inanition the gastro-intestinal tract taken as a whole manifests a marked growth capacity in rats starved shortly after birth. Stewart (1918a) found that the intestines gained 40 per cent in weight in rats kept at a constant birth- weight for an average of 16 days. In two other groups, underfed from birth to 3 weeks of age and from birth to 10 weeks of age, Stewart (1918) found that the gastro-intestinal tract gained 17 and 100 per cent, respectively.

Jackson (1915«) also found that the gastro-intestinal tract gained 28 per cent in rats underfed from the age of 3 to 10 weeks. However, in cases ol chronic inanition in rats underfed from the age ol 3 weeks to 1 year (Stewart, 1918) and from the age of 10 weeks to 8 months (Jackson, 1915a), there is a loss in the gastro-intestinal tract of 27 and 26 per cent, respectively.

In adult rats, during both acute and chronic inanition, there is a marked decrease in the gastro-intestinal tract, both filled and empty, the loss being about 57 per cent in each group (Jackson, 1915).

Stomach

As described under the section on materials and methods, the stomach in the test rats and controls was weighed as a separate organ, instead of being included with the intestines and pancreas as the gastro-intestinal group. However, the stomach and intestines were removed and weighed full and empty in a group of four normal newborn rats (average body-weight 5.0 grams) . The average weight of the stomach and intestines with their contents was 0.317 gram. Their weight, empty, was 0.128 gram, a value which agrees very well with that of Jackson (1913), who gives their weights with and without contents as 0.297 and 0.117 gram respectively.

The full stomach in my normal newborns had an average weight of 0.1198 gram (2.4 per cent of body-weight, 4.92 grams) . The empty stomach weighed 0.020 gram or 0.41 per cent of the body-weight. Hatai (1918) gives the weight of the empty stomach as 0.030 gram or 0.70 per cent of the body-weight, 4.2 grams. This value is considerably higher than mine, probably due to a variation in technique.

In my prenatal controls, the full stomach forms 0.7, 1.5, 1.5, 1.2, and 1.8 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the full stomach in the prenatal controls is much less than that in the normal newborn rat. The small relative weight of the full stomach in Group I agrees with the observations of Jackson (1909) that in the human fetus the relative weight of the stomach with contents is at first but little larger than that for the empty stomach.

The full stomach in my test rats forms 1.9, 1.5, 1.5, 1.3, and 1.0 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the full stomach is greater in the smaller test rats, while the converse is true of the prenatal controls.

The absolute weight of the full stomach is variable, averaging 3.7 per cent less in the test rats than in prenatal controls (see table 5) .

The empty stomach in my prenatal controls forms 0.31, 0.37, 0.39, 0.37, and 0.38 per cent oi the body-weight in Groups I to V, respectively (computed from table 5) . Thus the relative weight of the empty stomach in the prenatal controls is slightly less than that of the normal newborn rat, the difference in relative weight being most marked in Group I.

In my test rats the empty stomach forms 0.34, 0.38. 0.40, 0.38, and 0.39 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus, with the exception of Group I, there is very little difference in the relative weight of the stomach in the test rats and in the prenatal controls.

In the largest rats (Group V) the stomach (in both the test rats and prenatal controls) has practically the same relative weight as in the normal newborn rat. Thus the normal relative weight of the stomach is disturbed very little by prenatal inanition. The stomach in the test rats shows an average of 5.6 per cent in absolute weight above the prenatal norms. The difference is most marked in Group I (the smallest rats), where the absolute weight in the test rats is 15 per cent above that of the controls (table 5).

Pancreas

In postnatal inanition experiments on rats no direct observations have heretofore been made on the weight of the pancreas. Therefore no comparisons can be made with postnatal results.

Hatai (1918) gives the weight of the pancreas in the newborn rat as 0.0193 gram, or 0.45 per cent body-weight, 4.25 grams. In my normal newborns the weight of the pancreas is 0.0224 gram, or 0.45 per cent body-weight, 4.92 grams.

In my prenatal controls the weight of the pancreas forms 0.35, 0.38, 0.35, 0.45, and 0.42 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus, in the smaller prenatal controls (fetuses) the pancreas has a lower relative weight than in the larger rats (fetuses) in which the pancreas has approximately the same relative weight as in the normal newborn rat.

In my test rats the average weight of the pancreas forms 0.31, 0.37, 0.42, 0.37, 0.46 per cent of the body-weight in Groups I to V, respectively (computed from tableS). Thus in the test rats, as in the prenatal controls, the pancreas in the smaller rats forms a lower percentage of body- weight than in the larger rats, in which the pancreas has a relative (percentage) weight about the same as that in the normal newborn rat; but the weight of the pancreas is extremely variable in its individual weight and average absolute weight throughout all the groups (see table 5).


In Group I the absolute weight of the pancreas in the test rats is less by 10 per cent than in the prenatal controls; in Group II it is 2 per cent less; in Group III it is 20 per cent heavier; in Group IV, 16 per cent lighter; while in Group V it is 9 per cent heavier. The average for all groups shows a deficit of 0.2 per cent in the test rats.

From the above it is seen that the weight of the pancreas is very variable. Its low weight in one group is balanced by its high weight in another. Prenatal inanition probably has very little effect upon the relative weight of the pancreas, as its average weight in the test rats is but 0.2 per cent below that in the prenatal norms for the various groups.

Suprarenals

The weight of the suprarenals, according to the Wistar norm (Donaldson, 1915) , is0.0017 gram for a rat of 5.1 grams, or 0.034 per cent of the bodyweight. Jackson (1913) gives the weight of the suprarenals in the newborn as 0.0019 gram (0.00188), or 0.039 per cent of the body-weight. In my normal newborns the weight of the suprarenals averages 0.0016 gram or 0.032 per cent of the body-weight, 4.92 grams.

The weight of the suprarenals in my prenatal controls forms 0.044, 0.050, 0.048, 0.049, and 0.045 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus the relative weight of the suprarenals in the prenatal controls markedly exceeds that of the normal newborn rat.

In my test rats the average weight of the suprarenals forms 0.026, 0.023, 0.022, 0.024, and 0.024 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus it is evident that the relative weight of the suprarenals in the test rats is less than one-half that in the prenatal controls. On the other hand, however, their relative weight in the prenatal controls greatly exceeds their relative weight at birth. Thus, in the prenatal norm fetuses studied (2.19 to 4.19 grams), the suprarenals are relatively larger than at birth. They are probably still larger, relatively, in earlier stages, although no data from their earlier size in the rat are available. Jackson (1909) found that in the human fetus the suprarenals increase rapidly to their maximum (relative volume) in the third fetal month, after which they decrease steadily in relative size.

In the test rats the suprarenals show an average weight 52 per cent below that of the prenatal controls (table 5). The excessively weak growth-tendency of the suprarenals during fetal inanition can not be explained as due to any peculiarity ol their normal growth in rats at this time, for, as shown above, the prenatal controls maintain a nearly constant relative (percentage) weight during this period.

In postnatal inanition Stewart (1918a) found that in rats kept at birth-weight for 16 days the suprarenals gained 5 per cent in absolute weight over newborn controls, but with longer periods of starvation (underfed from birth to 3 weeks, body weight 10 grams), he found that the suprarenals increased markedly in weight (60 and 114 per cent, respectively).

Jackson (1915a) also found that the suprarenals manifested a marked growth tendency in young rats underfed from the age of 3 weeks to 10 weeks, the suprarenals gaming 26 per cent. Stewart (1918) , in chronic inanition in young rats, found that the suprarenals gained 48 per cent in absolute weight, while Jackson (1915a) found that the suprarenals lost during chronic inanition (26 per cent). In adult rats there is very little or no loss of absolute weight of the suprarenals during either acute or chronic inanition (Jackson, 1915).

From these observations it would appear that the suprarenals in the rat have a weak growth tendency during inanition in prenatal life and that it is still slight up to 16 days of age, reaching its maximum at a period between this time and 10 weeks, and declining thereafter.

Kidneys

Jackson (1913) found the kidneys in the newborn rat to weigh 0.46 gram or 0.97 per cent of the body-weight. The Wistar norm (Donaldson, 1915) for the kidneys in the newborn is 0.48 gram, or 0.97 per cent of the body-weight, 4.95 grams; in my normal newborns the weight of the kidneys is 0.46 gram or 0.94 per cent of the body-weight, 4.92 grams.

In my prenatal controls the weight of the kidneys forms 0.58, 0.63, 0.54, 0.71 and 0.70 per cent of the body-weight in Groups I to V respectively (computed from table 5). Thus in the prenatal controls the relative weight of the kidneys is less than that in the normal newborn rats. The difference decreases, however, from the small to the larger rats (fetuses). Therefore it is evident that in the rat fetus (from 2 to 4.1 grams) the kidneys are growing faster than the body as a whole.

In my test rats the average weight of the kidneys forms 0.56, 0.67, 069, 0.67, and 0.71 per cent of the body-weight in Groups I to V respectively (computed from table 5). There is very little difference in the relative weight of the kidneys in the test rats and the prenatal controls, but in neither have the kidneys reached the relative (percentage) weight of the body which is normal at birth. In both, the kidneys are growing faster than the body as a whole.

The absolute weight of the kidney is variable. Comparing the test rats and the prenatal controls (table 5), it is seen that in some groups the absolute weight is higher in the test rats, in others in the prenatal controls. This makes the results seem of questionable significance. Tins variability can not be attributed to errors in technique, however, as the kidney is an organ easy to remove and clean. In the test rats the absolute weight of the kidneys shows an average weight of 6 per cent above the prenatal controls.

This increase of 6 per cent in the absolute weight of the kidney during prenatal inanition is not nearly so marked as that noted in young rats underfed for various periods after birth. Stewart (table 6) found that the kidneys showed a gain of 90 per cent in absolute weight in rats kept at a birth-weight for an average of 16 days; this gain was less marked if the underfeeding was prolonged to 3 weeks, being 21 per cent (Stewart, 1918) . In rats underfed from birth to 10 weeks the kidneys showed a gain of 38 per cent. In rats underfed from the age of 3 weeks to 10 weeks, however, Jackson (1915a) found that the kidneys increased but 4 per cent; and in chronic inanition in young rats, where the starvation was begun from 3 to 10 weeks after birth and continued to 8 months or a year (Jackson, 1915a; Stewart, 1918), the kidneys showed a slight loss in weight.

In both acute and chronic inanition in adult rats the kidneys lose in weight relatively slightly less than the body as a whole (Jackson, 1915).

Testes and epididymides. — The Wistar norm (Donaldson, 1915) for the weight of the testes in the newborn rat is 0.004 gram or 0.081 per cent of the body-weight, 4.9 grams. Stewart (1918a) gives the weight of the testes in the newborn as 0.0027 gram, or 0.053 per cent of the body-weight, 5.08 grams. In my normal newborn the average weight of the testes is 0.0029 gram, or 0.0G0 per cent of the body-weight, 4.92 grams. There are no prenatal control males in Group I, consequently no testes for comparison.

In my prenatal controls the weight of the testes forms 0.050, 0.047, 0.042, and 0.040 per cent of the body in groups II to V, respectively (computed from table 5). Thus the relative weight of the testes in the prenatal controls is considerably less than that in the newborn rat. It is to be noted that the relative weight is higher in the smaller rats and decreases as the birth-weight is approached. That is, the testes are lagging behind the body-growth as a whole. In order to reach the relative weight normal for the testes at birth, there must necessarily be a period of very active growth in the testes just before birth (in fetuses between the body- weights of 4.1 and 5 grams).

In my test rats the average weight of the testes forms 0.030, 0.052, 0.056, 0.048, and 0.050 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus the relative weight of the testes is slightly higher in the test rats than in the prenatal controls. In both, however, the relative weight of the testes is markedly below that in the normal newborn rat.

The absolute weight of the testes in the test rats averages 16 per cent above the prenatal controls (in 4 groups).

In postnatal starvation, the testes during the first weeks of life manifest a remarkable growth tendency. Stewart (1918a) found that the absolute weight of the testes in rats kept at a constant birth-weight for 16 days exceeded that of newborn controls by 374 per cent (table 6), which was the strongest growth tendency exhibited by any organ in the body. In rats underfed from birth to 3 weeks, the increase in the absolute weight of the testes above that of controls of the same bodyweight (10 grams) is less, being 188 per cent (Stewart, 1918). In a longer period of underfeeding (birth to 10 weeks), the testes show a gain in weight of but 51 per cent (Stewart, 1918) ; while in underfeeding from 3 weeks of age to 10 weeks the testes gain 34 per cent (Jackson, 1915a). With prolonged starvation, however, the testes may lose considerably (Stewart, 1918), or may show practically no change (Jackson, 1915a).

In both acute and chronic inanition, in adult rats, the testes lose at about the same relative rate as the body as a whole, the loss being slightly more marked in chronic inanition (Jackson, 1915). From the foregoing it appears that during inanition the testes have their strongest growth tendency just after birth, and that this tendency rapidly decreases with the age of the rat. The weaker growth tendency before birth is evidenced by the weight of the testes during prenatal inanition, which is only 16 per cent above that of the prenatal controls of the same body-weight,

Stewart (1918a) gives the weight of the epididymides as 0.001G gram in the newborn rat, body-weight 5.08 grams. Hatai (1918) finds that the weight of the epididymides is 0.0025 gram in the newborn, body-weight of 4.4 grams; in my normal newborns the weight of

the epididymides was 0.0012 gram, body-weight 4.92 grams. This weight is slightly below that given by Stewart and is less than half the value given by Hatai. This difference is probably due to a variation in technique used in cleaning the organ.

There were no male prenatal controls in Group I (table 5) .

In the other groups the absolute weight of the epididymides in the test rats is considerably above that of the prenatal controls, with the exception of Group III, where it is 12 per cent below. The epididymides, however, average 17 per cent higher in the test rats of the various groups. This is about the same as the relation noted in the testes.

In postnatal inanition the epididymides, like the testes, show their strongest growth tendency shortly after birth (Stewart, 1918, 1918a); this, however, disappears earlier in the epididymides than in the testes (see table 6) .

Ovaries .—Jackson (1913) gives the weight of the ovaries in the newborn rat as 0.00078 gram, body-weight 5.0 grams. Stewart (1915a) found their weight to be 00110 gram' in the newborn with a body-weight of 4.98 grams. In my normal newborns the weight of the ovaries was 0.00060 gram, body-weight 4.98 grams. This lower weight for the ovaries in my series is probably due to a variation in technique, since it is very difficult to free the ovary from its capsule and from the

Fallopian tube.

The data on the ovaries are somewhat irregular and conflicting (table o). In Groups I and II the absolute weight of the ovaries in the test rats exceeds that in the prenatal controls by 68 and 6 per cent, respectively; in Group III it is 37 per cent below in Group IV it is 2.5 per cent above; in Group V, 33 per cent below. The average weight is 1 .3 per cent higher in the test rats. It is hazardous to draw any conclusions from such irregular data, but probably the ovary is very little affected by prenatal inanition. .

It is interesting to note, however, that the ovaries in postnatal inanition, in general, show a tendency to increase in weight, This tendency is very slight shortly after birth, since in young rats kept at a constant birth-weight for 16 days the ovaries showed a gain of but 5 per cent in absolute weight above the controls (Stewart 1918a) In rats underfed from birth to 3 weeks the ovaries showed a gain of 83 per cent, and in rats starved from birth to 10 weeks the gain is 54 per cent, Stewart 1918). In rats kept at a constant body-weight from 3 to 10 weeks of age the ovaries lose 27 per cent (Jackson, 1915a) . In longer periods of inanition Stewart (1918) found a gain of 17 per cent in the weight of the ovaries, while Jackson (1915a) found a loss of 54 per cent. It should be remarked, however, that Jackson began the underfeeding at 10 weeks instead of at 3 weeks, as in Stewart's series.

From these data it may be concluded that in prenatal life and up to a few days after birth, the growth tendency in the ovary during inanition is very slight; but that it soon reaches a maximum at a period between 2 and 3 weeks of age, declining later.

Thyroid. — The Wistar norm (Donaldson, 1915) for the weight of the thyroid gland is 0.00145 gram, or 0.027 per cent of the body-weight, 5.1 grams. Jackson (1913) gives the weight of the thyroid as 0.0012 gram, body-weight 5.1 grams. In my normal newborn series the thyroid weighed 0.0011 gram, or 0.022 per cent of the body-weight, 4.92 grams.

In my prenatal controls the weight of the thyroid forms 0.040, 0.030, 0.032, 0.029, and 0.029 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . Thus in the prenatal controls the thyroid forms a relatively higher percentage of the body-weight than in the normal newborn. Since the relative weight of the thyroid decreases as the birth-weight is approached, it is evident that the body as a whole is growing faster than the thyroid.

In my test rats the thyroid forms 0.024, 0.020, 0.023, 0.021, and 0.016 per cent of the body-weight in Groups I to V, respectively (computed from table 5). Thus in the test rats the thyroid has about the same relative weight as in the normal newborn rat and a lower relative weight than in the prenatal controls.

That the thyroid has been inhibited in its growth in the test rats is evident from a comparison of the absolute weights (table 5) . The absolute weight of the thyroid in the test rats is 33, 28, 11, 29, and 45 per cent less than that in the prenatal controls in Groups I to V, respectively. Thus, the absolute weight of the thyroid is lower in all the groups, the average being 29 per cent.

In postnatal inanition the thyroid exhibits a tendency to gain slightly in weight in rats held at maintenance from birth to 16 days, or starved from birth to 3 weeks, or from birth to 10 weeks (Stewart, 1918, 1918a). In longer periods of starvation the thyroid loses quite markedly (Jackson, 1915a; Stewart, 1918).

In adult rats, during acute inanition, the thyroid suffers very little or no loss in weight, while during chronic inanition it loses relatively less than the body as a whole (Jackson, 1915).


Discussion

A comparison of the similarities and differences in the growth of the various organs and systems in both prenatal and postnatal inanition is so well shown in table 6 that a detailed discussion is deemed unnecessary. However, special attention will be called to certain points.

In the systems (see table 6) the "remainder" is constantly above normal in weight in prenatal inanition, while in postnatal inanition it shows a definite loss at various periods throughout the life of the rat.


The visceral group as a whole is subnormal in weight during prenatal inanition. In postnatal inanition, however, it shows a marked tendency to gain in weight in the younger rats (underfed from birth to an average of 16 days, and from birth to 10 weeks, Stewart, 1918a, 1918). When the underfeeding is begun at 3 weeks of age, the visceral group shows a slight gain or just maintains a growth equal to that of the controls. In cases of prolonged underfeeding in the young rats (under 1 year of age) and in adult life, the visceral group shows a decided loss. It should be noted, as before mentioned, that the gain or loss in the visceral group during inanition is dominated by a loss or gain in weight of the certain large organs, such as the liver, lungs, gastro-intestinal tract, and brain. In postnatal inanition the gain in the visceral group compensates for the loss in the "remainder," while in prenatal inanition the converse is true. Thus it is evident that the strongest growth tendency manifested by the visceral group during inanition is at a period just after birth and that it becomes progressively weaker thereafter.


The musculature has a subnormal weight in prenatal inanition and shows but a slight gain (musculature and skeleton combined) in rats underfed from birth to an average of 16 days of age (Stewart, 1918a). It is in rats underfed from birth to 3 weeks of age that the musculature manifests its greatest gain. This tendency to gain is present, but weaker, in rats underfed for longer periods (Jackson, 1915a; Stewart, 1918). In both acute and chronic inanition in adult rats the musculature loses in about the same proportion as the body as a whole (Jackson, 1915). It is evident, therefore, that the growth tendency in the musculature during inanition in the rat is weakest before birth, slightly stronger just after birth, and strongest at a period between birth and 3 weeks of age, declining thereafter.


The skeleton has a subnormal weight during prenatal inanition and shows a very slight gain in rats starved from birth to an average of 16 days. In young rats underfed for longer periods, up to adult life, the skeleton shows a marked tendency to gain. During inanition in adult rats the skeleton shows very little change in weight. Thus the growth tendency manifested by the skeleton during inanition is weakest before birth and slightly stronger from birth to 16 days of age. At 3 weeks of age, however, it is quite strong, increasing slightly toward adult life. It thus appears that the growth tendency manifested during inanition develops at a relatively later period in the skeleton then in the musculature, but persists longer in the former.


The integument manifests a moderately strong growth tendency during prenatal inanition and just after birth (in rats underfed to an average of 16 days of age) . In rats underfed from birth to 3 weeks of age the integument shows no gain, and inrats starved for longer periods it shows a constant loss in weight.


In postnatal inanition the organs as a general rule manifest their strongest growth tendency in the youngest rats (underfed from birth to an average of 16 days (Stewart, 1918a). The liver, suprarenals and ovaries are exceptions to this rule. The liver loses markedly at this period as compared with a gain at later periods. The suprarenals and ovaries show a very slight gain as compared with marked gain in later periods.


With but few exceptions, those organs which show the most marked gain in the newborn rats (underfed from birth to 16 days) during postnatal inanition are also above normal in prenatal inanition. The spinal cord is the only exception. Also, all the organs which show a loss or only a slight gain in the newborn rats during postnatal inanition (excepting the indefinite "remainder") are subnormal in weight in prenatal inanition.


It should be noted that the organs and systems that are above the normal weight in prenatal inanition have apparently a lower growth capacity than that shown in postnatal inanition just after birth (see table 6), while those organs and systems which are below normal weight in prenatal inanition (with the exception of the thymus) suffer a greater loss than in postnatal inanition. From the foregoing it is evident in general that the organs and systems of the rat have a weaker growth tendency during prenatal than during postnatal inanition.


The present investigations, therefore, emphasize the fact that in different periods in the life of the rat certain organs and parts react differently, as manifested by their growth during inanition. This is probably due mainly to the varying intensity of the normal growth tendency in the organs and parts at different periods.


Jackson and Stewart (1918) have called attention to the fact that during inanition in the rat the varying intensity of growth tendency in the different organs and systems depends on four factors: (1) the duration of the period of inanition, (2) the age at which it occurs, (3) its severity, and (4) the character of the inanition.


In prenatal inanition the duration is known (period of starvation of mother). The age is known (length of gestation). The severity is apparently that sufficient to retard the growth of the entire body, an average of 40 per cent as compared with normal newborn controls. Attention may be called to the fact that some of the apparent differences in the growth tendencies of the organs and parts during prenatal and postnatal inanition may be due to the difference in the relative retardation of the body-growth. That is, while the body-growth (average) was retarded 40 per cent in prenatal inanition, it was retarded 66 per cent in Stewart's (1918a) series in starvation just after birth. The real nature of the inanition, i. c, the amount of reduction in the various nutritive substances reaching the fetus during starvation of the mother, is unknown. The exact character of the inanition to which the fetus is subjected is, therefore, uncertain. However, from the nature of the changes in the relative weight of the organs and parts, it may be stated that the maternal organism during starvation in pregnancy makes extraordinary efforts, as is well known, to keep up the necessary supplies of nutritive substances to the growing fetus and thus protect it from the effects of inanition.


Summary

  1. Starvation instituted shortly after copulation in the female albino rat apparently results in an inhibition of pregnancy in the majority of cases. Whether this is due to an inhibition of the implantation, or to death of the ovum, has not been proved.
  2. Of 59 female albino rats starved from the eleventh day after copulation, early death of the fetus in utero occurred in 3 cases. Microscopic examination of the swellings in the uterine horns revealed a mass of degenerating tissue, with no evidence of any fetal structures.
  3. The length of gestation in the mothers starved during the last half of pregnancy varied from 21 to 26 days. Eight (of the 22 total) were above the 23-day normal limit, 6 with a gestation-period of 24 days, 1 of 25, and 1 of 26. The average p eriod of gestation was 23 days, or 1 day above the normal average.
  4. No abortions or premature deliveries were observed in any of the underfed rats.
  5. Of a total of 120 newborn from mothers starved during the last half of pregnancy, 41 were found dead after delivery. Whether these were dead in utero, or died during delivery or afterwards, is uncertain, since at birth they dropped through the wire bottom of the cage. Those living-born that were inclosed within the amniotic sac died of suffocation. Those found living seemed quite vigorous.
  6. The average number of observed young per litter, from mothers starved during the last half of pregnancy, was 5.9. (The normal average number of young per litter was 7.0 in 1,089 litters; King and Stotsenburg, 1915.)
  7. A condition of relative sterility apparently results in females starved during the last half of pregnancy. Of the total number starved but 4 became pregnant a second time.
  8. The average weight of the newborn from mothers starved severely during the last half of pregnancy was approximately 3 grams, or 40 per cent below the normal birth-weight of 5 grams.
  9. There was no constant relation between the percentage loss in weight of the mother and the weight of the newborn. In general, however, the largest females showed the largest relative loss in weight and bore the largest young; and the weight of the newborn tends to be inversely proportioned to the severity of the starvation.
  10. A prenatal norm for the various systems and organs was established by comparing the relative weights, at the various fetal stages, with those of the normal newborn.
  11. During prenatal inanition the tail grows in length faster than the remainder of the body, thus giving rise to relatively long-tailed individuals.
  12. Concerning the changes in the general body proportions during prenatal inanition, the head and limbs are slightly above normal weight, counterbalanced by a lower weight in the trunk.
  13. The observations on the various systems are summarized as follows: The "remainder" has a weight 25 per cent higher in the test rats than in the prenatal controls. The integument shows a weight averaging 10 per cent above normal in the test rats. The musculature and moist skeleton are slightly subnormal in weight in the test rats, being 5 and 7 per cent, respectively below the prenatal norm. However, the dried skeleton in the test rats has a weight 12 per cent above the prenatal norm. The visceral group, as a whole, has a markedly subnormal weight in the test rats, being 18 per cent below the prenatal norm. This is due chiefly to the subnormal weight of the liver and lungs. The low weight in the visceral group evidently compensates for the high weight of the "remainder."
  14. The weight changes observed in the individual organs in the test rats during prenatal inanition, as compared with normal fetuses of the same bodyweight, show the following average percentage differences in weight :
  15. In general, therefore, it may be stated that the spleen, eyeballs, epididymides, testes, and brain manifest a fairly strong growth tendency during prenatal inanition, the tendency decreasing in the order named. A slight growth tendency is manifested by the heart, kidneys, stomach, and ovaries, decreasing in the order named. A retardation in growth during prenatal inanition increasing in the order named is shown by the pancreas, spinal cord, intestines, thymus, thyroid, lungs, liver, and suprarenals.
  16. In general, the organs and systems that have been found to gain greatly during postnatal inanition (in the newborn rats) are, during prenatal inanition, also above normal weight, but to a much less degree; while those below or but slightly above normal weight during postnatal inanition show a still greater loss in prenatal inanition. Thus, during inanition, the growth impulse of the organs appears as a rule weaker in the prenatal than in the postnatal period. It should be noted, however, that the exact nature of the prenatal inanition is somewhat uncertain.


Tables

Table 1. Data on female albino rats starved (luring la.il half of pregnancy mid resulting litters.


1 Starved moderately for 11 days after copulation, then starved severely from eleventh to twenty-fourth day of pregnancy. Note: Rats B2 and B43 were underfed during two pregnancies.


Table 2. Data on rn gnanl female rats starved from eleventh day, death resulting.


Table 3. Female albino rats starred from the eleventh day after copulation, no litters resulting. Rat B 35 was 134 days old; age of others unknown.

Table 4. Individual data for rats dissected.


Table 5. Autopsy data showing changes in average body-length, tail-length, and average weight of the various systems and organs in newborn albino rats (test rats) from mothers underfed 'hiring the last half of pregnancy, as compared with prenatal control fetuses of the same average body-weight.



Table 6. Average percentage changes in weight of systems and organs in albino rats during prenatal and postnatal inanition. Normal control fetuses of same body-weight used for comparison with newborn from mothers underfed during last half of pregnancy. In postnatal inanition, younger normal controls of same body-weight were used, excepting the adult rats where controls of the same initial body-weight were used.


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