242 Herrino^ 



& 



tion of the male thymus. A few measurements made in another series of 

 male animals support this view, but the difference is too small to be of any- 

 special significance. 



In the females the figures show an average rise of 7 to 11 per cent, in 

 the weight of the thymus of the thyroid-fed animals. The delayed involu- 

 tion in the female rat is not constant, and the figures are quite capable of 

 explanation by normal variability. 



Hoskins found that the thymus of his thyroid-fed female rats averaged 

 10 per cent, lighter than the thymus of the controls. In males there was 

 no definite change. Hoskins concludes that thyroid-feeding has no 

 constant effects upon the thymus, and my figures also support this 

 conclusion. 



8. The Testes. — The testes show variations in weight, but not to 

 anything like the extent characteristic of other organs, such as the liver, 

 spleen, and thymus. No data are available for comparison in Donaldson's 

 tables, because in his figures the epididymis is included with the testis. 

 The epididymis shows large variations, and there is no advantage gained 

 by including it with the testis as a single unit. 



The thyroid-fed animals in my series show slightly heavier testes than 

 the controls, the increase being 8 per cent, per unit body weight, and 

 5 per cent, per unit body length. Hoskins also obtained an increase of 

 weight of the testes of his thyroid-fed animals, the enlargement amounting 

 to 7 per cent, in the older animals, and 13 per cent, in the younger. In 

 my series of control rats the first two animals have exceptionally small 

 testes, and if they are excluded there is little difference between the 

 averages of the remaining animals of the two groups. Hoskins attached 

 no special significance to the increase of weight. The fact that our figures 

 vary in the same direction may point to a slight influence of thyroid in 

 Accelerating the growth of the testes. Iscovesco also noted the same 

 action. The acceleration is only small, and lies within the normal limits 

 of variation. It is unlikely, therefore, that it can be ascribed to any direct 

 action of thyroid, and is merely the result of increased metabolism. In 

 my series it is associated with a somewhat hastened involution of the 

 thymus, but in Hoskins' rats this is not the case. 



9. The Ovaries. — The ovaries are liable to extreme variations in size, 

 and a systematic examination of a larger number of animals than is included 

 in this series is necessary to afford any sound conclusions as to the signifi- 

 cance of changes brought about by thyroid-feeding. The ovaries of the 

 thyroid-fed animals average 12 to 14 per cent, heavier than those of the 

 control rats. This increase, it will be noticed, is associated in these animals 

 with a seemingly delayed involution of the thymus. 



Hoskins obtained no constant results in his thyroid-fed animals. 

 Iscovesco reported hypertrophy as the result of his ether-soluble extract 

 of thyroid. 



The figures given in my records do not indicate that thyroid has any 



