248 Herring 



observations, however, are not sufficiently numerous to warrant any criticism 

 of Hoskins' results with regard to changes in the male pituitary. 



No constant changes are demonstrated in the thymus. Its involution 

 appears to have been somewhat accelerated in males, and somewhat delayed 

 in females in my series of animals, but the changes are slight and may be 

 merely accidental. 



The testes show some increase in weight, as also do the ovaries. The 

 hypertrophy of the latter is not nearly so great in my animals as in those 

 of Hatai's as the result of muscular activity. 



Iscovesco obtained great hypertrophy of the uterus of the rabbit by 

 injections of an ether-soluble extract of thyroid. In only one rat of my 

 series can hypertrophy of the uterus be detected, and this is in the largest 

 animal of the series. This rat has a comparatively large pituitary body, 

 the heaviest suprarenals, and the largest adrenalin content of any animal 

 in my series. In the other animals the growth of the uterus is strikingly 

 inhibited by thyroid-feeding, and this lack of growth appears to be 

 associated with a corresponding lack of growth of the pituitary body. It 

 is suggestive of a relation between the two, and the diminished growth of 

 the pituitary bod}^ may in young animals be the cause of the diminished 

 growth of the uterus. 



V. Summary of Conclusions. 



Small doses, O'l to 0'2 grm. of fresh ox thyroid given daily in food to 

 growing white rats, have little effect upon the growth as estimated by 

 body length, but tend on the whole to diminish the growth as estimated by 

 body weight. In this respect my results confirm those obtained by 

 E. R. Hoskins. 



iVmale rats are more susceptible to the action of thyroid than 

 rats. 



Thyroid-feeding causes profound changes in many of the organs of the 

 body, and eventually, in the doses mentioned, leads to fatal results. 



Thyroid-feeding stimulates metabolism, leads to the rapid disappear- 

 ance of glycogen from the liver as stated by Cramer and Krause, and to 

 a general loss of fat from the body as noted by numerous observers. The 

 diminution in body weight caused by the loss of fat may for a time be 

 counterbalanced or even more than counterbalanced by the increased weight 

 of many of the viscera. 



My results agree with those of Hoskins in that thyroid-feeding is 

 found to produce enlargement of the suprarenals, heart, liver, spleen, testes 

 and ovaries ; no constant changes in the thymus, and a decrease in size of 

 the pituitary body in female rats. They also confirm Kojima's statement 

 that thyroid-feeding produces hypertrophy of the pancreas. 



The thyroid glands of thyroid-fed animals are decreased in weight, and 

 show signs of relative inactivity. 



My results differ from those of Hoskins mainly in the greater extent 



