EFFECTS OF INANITION IN THE PREGNANT ALBINO RAT. 117 



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 be- 

 comes 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 body- 

 weight (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 body- 

 weight 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 



