222 BENJAMIN 1 HORNING AND HARRY BEAL TORREY. 



this was especially true when the dosage was sufficiently large to 

 induce structural defects in the vane as well. Similar defects 

 could be produced by inanition alone. Furthermore, defective 

 pigmentation appeared in birds that were not on a thyroid diet 

 and showed no general signs of hyperthyroidism. When such 

 defects in pigmentation appeared in birds receiving the dosage 

 of thyroid commonly employed by us, namely, I gram of Armour 

 and Company's desiccated thyroid to 5,000 grams of body weight, 

 the non-pigmented areas, when they occurred at all, were usually 

 limited to the tips of the feathers involved. This was strictly 

 true for the feathers of the trunk. In wing quills, the extent of 

 the defect was sometimes larger. 



With these facts in mind, we are disposed to refer the striking 

 change in plumage recorded by Zavadovsky to a metabolic 

 disturbance induced by an excessive, essentially toxic dosage of 

 thyroid rather than to a specific action of the latter on the 

 pigment-forming mechanism. The results of the graft mentioned 

 in his second paper are not unfavorable to this view. We have 

 not seen the extraordinary casting of feathers in adult birds 

 which we suspect of being a further sequel of toxic feeding. 

 But the moulting process, like the pigment-forming mechanism, 

 is subject to modification under the influence of non-toxic doses 

 of thyroid. This has been referred to in a preliminary note 

 (Horning and Torrey, 1923, 2) and considered more fully in a 

 recent paper (1925, i). In the latter, two kinds of results of 

 thyroid feeding were discriminated, the one referable to nutritive 

 (associated with toxic), the other to non-nutritive factors. And 

 shortly after (1925, 2), changes in feather structure were described 

 which were not referable to changes in nutrition or to intoxication. 



In the present paper, another non-toxic, non-nutritive effect of 

 thyroid feeding will be described, namely, an increased pigmenta- 

 tion. Whereas Zavadovsky 's birds blanched and not infrequently 

 died under the massive doses pressed upon them, our birds, 

 with a daily ration of thyroid that permitted them to maintain 

 their health, lay viable eggs and rear normal offspring, grew 

 darker. 



