GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 329 



influenced in size by diet, etc. One might expect a relatively 

 larger liver in the female, which is said to be more active than 

 the male (Slonaker '12), since exercise has been shown to cause 

 hj^Dertrophy of this organ (Hatai '15). Jackson ('13) found 

 the liver heavier in the male, however, and this is apparently 

 true also for my control animals. 



b. Thyroid groups. In the thyroid-fed groups, (tables 8 to 

 10) the liver appears relatively considerably heavier than in the 

 controls. When compared according to Donaldson's method, 

 the females show an increase in the absolute weight of the liver 

 of 26.7 per cent and 30.5 per cent for the older and younger 

 groups respectively, and the males show a corresponding in- 

 crease of 24.4 per cent and 6.4 per cent. The apparently small 

 increase in the weight of the liver of the younger males is 

 probably to be explained by the fact that the liver is unusually 

 heavy in the corresponding control group. Even when due al- 

 lowance for normal variabiUty is made, a hypertrophy of the 

 liver due to thyroid feeding is therefore strongly indicated. 



c. Thymus, hypophysis, and pineal groups. In all the younger 

 groups of females the liver averages larger than in the controls, 

 but as no corresponding difference is found in the other groups, 

 the variation is probably not significant. 



13. Spleen (tables 4 to 10) 



a. Controls. As appears by comparing the individual data, 

 the absolute weight of the spleen in the control groups is from 

 30 per cent to 100 per cent higher than the figures for corres- 

 ponding animals in Donaldson's Wistar tables. In the latter 

 tables, however, the figures for the spleen are derived from 

 the formula of Hatai ('13) who used data from which the 'en- 

 larged' spleens had been excluded. Whether these tables for 

 the spleen really represent the true norm is therefore question- 

 able, since it is not known whether the 'enlarged' spleens are 

 actually pathological, or represent merely extreme cases of 

 normal variation in size. Jackson ('13) found the variability 



