85 
Although the amounts of thyroid fed varied widely (from 0.001 
gm. to 0.007 gm.), there was approximately the same amount of 
iodine in all cases and, with one exception, the lowering of the resist- 
ance seemed to be about equal. In all cases except one fully ten 
times as much morphine was required to kill the controls as to kill 
those which had received thyroid. The thyroid caused practically no 
loss of weight; the very slight loss which occurred can be attributed 
to the cracker diet. 
SUMMARY OF EXPERIMENTS ON RATS. 
The above experiments show very clearly that the resistance of 
rats to morphine is lowered by the feeding of thyroid. In two 
series the fatal dose for the thyroid-fed rats was but one-tenth that 
for the controls. They also show that the activity of different 
thyroid preparations in this respect is closely paraflel to their iodine 
content. It would doubtlessly be possible to determine with a fair 
degree of accuracy the percentage of iodine in a thyroid preparation 
by comparing its physiological activity with that of another prepara- 
tion containing a known percentage of iodine. The increased 
susceptibility to morphine is entirely independent of any loss of 
weight; it can evidently not be attributed to a “general lowering of 
resistance” such as may be supposed to occur when there is a loss of 
weight from starvation.® 
6. — Experiments on Mice. 
The results of the experiments on mice were somewhat irregular. 
There was invariably, however, an increased susceptibility to mor- 
phine as a result of the feeding of thyroid. As a rule the thyroid 
containing the larger percentage of iodine had the greater effect 
but there were many exceptions which we are unable to explain. 
It would probably be impossible to detect small variations in the 
percentage of iodine in different thyroid preparations from their 
effects upon the resistance of mice to morphine. 
As these experiments do not offer many points of special interest 
they will be reproduced in abstract only. The average loss of 
weight, expressed in percentage of original weight, is given in the 
last column. 
a Starvation markedly increases the resistance of animals to some poisons; this is 
the case, for example, with acetonitrile. (See R. Hunt, Studies in Experimental 
Alcoholism, Bull. 33, Hygienic Laboratory, 1907, p. 34.) 
