244 Herring 



Institute rat. Hoskins also found a lighter series of thyroids in his 

 animals, and ascribes the difference to differences of technique employed 

 in their removal. In my series the thyroids were carefully dissected out, 

 examined with a strong lens, and the outl3"ing fat and connective tissue 

 removed. 



Thyroid-feeding gives a reduction in weight of the thyroids in my series 

 of 21 to 24 per cent. A similar but rather larger loss of weight occurs in 

 the thyroids of the thyroid-fed males examined. The loss of weight is a 

 very constant phenomenon, and I have observed the same thing in the 

 thyroids of thyroid-fed cats. Histological changes also are constant and 

 striking. The thyroids of the thyroid -fed animals present vesicles con- 

 taining a denser and more stainable colloid, but the chief difference lies in 

 the cellular elements of the thyroids. In the thyroid-fed animals the cells 

 are thin and flattened, whereas in the control animals the cells are more 

 numerous and cubical. The flattened cell appears to be associated with 

 decreased activity of the gland, the cubical cell and comparatively little 

 colloid with the more active type of gland. 



Hoskins noted no constant changes, though his figures, resulting from 

 much smaller doses of thyroid, do not contradict mine. From the evidence 

 adduced it seems clear that thyroid-feeding inhibits to some extent the 

 action of the animals' own thyroids, and in growing animals checks the 

 simultaneous growth of these glands. Iscovesco found enlargement of 

 the thyroids, but he used ether-soluble extracts, and his experiments do 

 not necessarily afford a fair comparison with those in which thyroid itself 

 is used. 



12. The Pituitary Body. — The weights of the pituitary body of the 

 female control rats recorded in the tables agree fairly well with Donaldson's 

 figures, but average rather less per unit body weight. The pituitaries of 

 the male animals were not recorded but were preserved for histological 

 examination attached to the base of the brain. A few additional observa- 

 tions have been made on male animals, but are not as satisfactory as they 

 might be owing to the great loss of body weight which occurred in the 

 thyroid-fed animals of the same litter. The pituitaries of the male controls 

 are rather lighter j)er unit body weight than those of the females. This 

 difference between the male and female pituitaries was noted by Hatai (8), 

 and is shown in Donaldson's tables. It is also seen in Hoskins' figures. 



Hoskins found that the administration of small amounts of thyroid 

 checks the growth of the pituitary body in the female rat, and accelerates 

 it in the male. He obtained a decrease of weight of 8"8 to 11 '5 per cent, in 

 females, and an increase of weight of 18 to 21-3 per cent, in males. My 

 figures confirm Hoskins' results with regard to the females, and partly, 

 but not entirely, with regard to the males. In the female thyroid -fed 

 rats my results are almost identical, the pituitary showing an average 

 decrease in weight of 11 per cent, when measured per 100 grm. body 

 weight, and of 8 per cent, when measured in terms of body length 



