E. B. Hart and H. Steenbock 315 
a trace or none to a percentage in the thousandth place, as 
for beans 0.0002 per cent, wheat 0.0008 per cent, and rarely 
reaches a thousandth of a per cent, although corn stover showed 
0.0012 per cent and celery 0.0016 per cent, it is equally true that 
the iodine content of the normal thyroid is relatively low. The 
normal fresh thyroid of a 300 pound pig will weigh about 50 gm., 
equivalent to about 7.5 gm. of dry matter with 0.2 per cent of 
iodine or 15 mg. In 100 pounds of feed with 0.0002 per cent of 
iodine there are 90 mg. of iodine, or six times that of a normal 
swine thyroid. The rate of metabolism of the thyroid colloid is 
unknown. The wonderful avidity of thyroid tissue for iodine, 
as lately demonstrated by Marine and Feiss and Marine and 
Rogoff,> makes it appear more than probable that it is not, at 
least in all cases, a deficiency of iodine in the feed per se, that is 
the primary cause of thyroid hyperplasia in swine producing hair- 
less pigs, but that the problem is more complex and related to the 
absorption of iodine from the digestive tract or by the thyroid 
gland itself. 
We have successfully corrected the malady of hairless pig pro- 
duction by the use of potassium iodide, but would hesitate to pre- 
scribe potassium iodide as a necessity for normal reproduction for 
all regions and all animals. The same feeds that produce hairless 
and dead pigs can be so combined as to produce normal pigs. 
What the problem needs is a fundamental study of all the factors 
that may contribute to the final condition of a deranged thyroid 
gland and its accompanying faulty metabolism. If certain un- 
known conditions are favorable a sow may obtain from natural 
feeds the iodine required for both her own and the fetal thy- 
roids, but if unknown and unfavorable conditions prevail the ani- 
mal may obtain barely enough for her own thyroid activity, but 
not enough for fetal thyroid development.. We have not com- 
pleted our studies of the problem, but what information we have 
accumulated is offered as a preliminary report. 
5 Marine, D., and Feiss, H. O., J. Pharm. and Exp. Therap., 1915, vii, 
557. Marine, D., and Rogoff, J. M., zbid., 1916, viii, 4389. 
