286 
Journal of Agricultural Research 
Vol. XXIX, No. 6 
eluded on May 2. On February 20, a 
patch of feathers was pulled from the 
cape and wing bow of each bird and 
saved for future reference. (See PI. 1.) 
On March 1, a patch from the saddle and 
one sickle feather were also pulled. All 
birds were weighed weekly and notes 
were kept on general health and on 
growth of new feathers. Such results 
as were obtained may be stated 
briefly. 
There was considerable variability 
in the rate at which new feathers 
replaced those which were pulled, 
depending in part, apparently, on the 
state of health of the individual bird, 
but also, as will be noted later, on the 
medication. In the better-developed 
cases the new feathers were of full 
length by May 2, but in the others 
comparatively little replacement had 
occurred. In no case was the sickle 
replaced. 
It will simplify matters to make the 
summary statement that in all lots 
except that receiving thyroids the new 
feathers were in all respects normal 
both as to shape and coloration. This 
is doubtless what was to be expected, 
since experiments on mammals have 
shown little effect caused by adminis¬ 
tering iodine, free or in inorganic 
combination, except in cases of iodine 
deficiency or of subnormal activity of 
the thyroid gland. There is no reason 
to suppose that either of these condi¬ 
tions existed in the present instance. 
The new feathers on the thyroid-fed 
birds were, however, strikingly different 
from those which were pulled, as is 
indicated in the accompanying tabula¬ 
tion. There was considerable varia¬ 
tion, as will be noted, and it can not 
be said that the replaced feathers were 
characteristically female. As relates to 
color, there was an evident action to¬ 
ward the reduction of red pigment, 
varying in degree in the different 
birds, but tending to be arranged in 
“stippling’’ when present. This was 
particularly true in the new cape 
feathers of bird No. 441, which were 
decidedly femalelike in appearance. 
In all cases the red was broken and 
much more irregular in distribution 
than in normal male feathers. The 
resemblance to female feathers was 
much more striking in respect to shape 
and structure, the broad, rounded ends 
contrasting strongly with the pointed 
tips of the male plumage on these 
parts. Furthermore, the great reduc¬ 
tion or absence of the zone of “free” 
barbs, that is, of barbs lacking bar- 
bules and hooks, so characteristic of 
the normal male feathers, was very 
evident, and constitutes another re¬ 
semblance to female plumage. 
Summing up, it may be said that 
the feeding of desiccated thyroids to 
male Brown Leghorn fowls in certain 
amounts profoundly modifies feathers 
grown while the material is being 
administered. The feathers produced 
under these conditions are not typically 
female in type, but they do show distinct 
female characteristics. There would 
seem to be in this case no question of 
altering the sex of the bird, nor in all 
probability of the sex hormones. Nor 
is it likely that the administered 
thyroid material acts through the 
mediation of the thyroid gland of the 
bird. It seems altogether more prob¬ 
able that the thyroid fed acts directly 
in influencing the metabolism of the 
developing feather germ. The very 
evident tendency to an increased 
melanism may indicate a higher oxida¬ 
tion of the pigment products; the 
explanation of the change in form must 
be less direct. 
The feeding of iodine, free and in 
inorganic combination, gave no result 
comparable to that obtained from des- 
sicated thyroids containing an equiva¬ 
lent amount of iodine. 
One other apparent effect of the 
thyroid feeding deserves mention, 
namely, that the replacement of 
feathers on the birds receiving thyroids 
was noticeably more rapid than on the 
others. Since some of the birds were 
suffering from “colds” and were not 
in the best of health during the trial, 
however, it would not be safe to make 
too definite a pronouncement on this 
point. If the feeding of thyroid should 
prove to have a stimulating effect on 
feather development it might prove 
useful in inducing quick and uniform 
molting, a factor of considerable prac¬ 
tical importance. It is proposed to test 
this further by later experiments. 
EXPLANATORY LEGEND FOR PLATE 1 
A, B, and C — Normal feathers from saddle, cape, and wing bow, respectively, of bird No. 448. Cape 
and wing bow feathers pulled February 20; saddle, March 1. 
D, E, and F.—New feathers grown by bird No. 448, replacing those pulled (D, wing bow; E, cape; F, 
saddle). The new feathers, which were pulled on May 2, appear normal in shape, structure, and coloration, 
apparently not having been affected by the free iodine in alcoholic solution administered to this subject. 
G, H, and I—New feathers (May 2) from saddle, cape, and wing bow, respectively, from bird No. 441. 
These feathers show modification of shape, structure, and coloration, approaching the female type in these 
Tespects. The stippling in the cape feather is closely similar to that which occurs in females. These 
modifications are attributed to the desiccated thyroids fed. 
J and K.—New cape and saddle feathers from bird No. 444, following feeding of desiccated thyroids. The 
melanistic effect was especially pronounced in this bird. 
