GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 319 



ture is inadequate to remove all the moisture. More data are 

 needed to establish a satisfactory norm. 



6. Thyroid groups. The skeleton appears slightly heavier 

 for the thyroid treatment in the average of the younger groups. 

 A comparison of the individual data shows that both wet and 

 dry skeletons average somewhat heavier in most of the rats 

 receiving higher dosage of thyroid than in those of low dosage 

 and controls. This suggests that the thyroid treatment may 

 perhaps tend to stimulate skeletal development, as claimed 

 by Bircher ('10b). However, the possibility of errors from ac- 

 cidental variations must be kept in mind, as the differences 

 found are not very great, and were not constant in every litter. 



c. Thymus, hypophysis, and pineal groups. The various 

 groups fed thymus, hypophysis and pineal glands show no im- 

 portant or constant variation from the controls in regard to 

 the skeleton. If any effect was produced, it is so slight as to 

 be masked by normal variation. 



6. Brain {tables Jf to 10) 



. a. Controls. As shown by tables 4 and 5, the absolute weight 

 of the brain does not vary greatly from that shown by Donalds, 

 son's tables for rats of similar sex and body weight or body 

 length. 



In percentage weights, as might be expected, the males have 

 relatively lighter brains than the females, and the older brains 

 average lighter than the younger, on account of the fact that 

 the brain lags behind in the growth of the body. 



h. Thyroid groups. On comparing directly the average rel- 

 ative (percentage) weights (tables 8 and 9) of the controls (mus- 

 cle-fed) and thyroid-fed animals, the brain in the latter appears 

 slightly heavier in all except the younger group of males; but 

 on comparing the absolute weights with the Wistar norms for 

 animals of corresponding body weight, it is found that the dif- 

 ference in the various litters is not constant and the brain of 

 the thyroid-fed rats averages even smaller than the normal 

 (table 10). 



