87 
With the increased percentage of iodine in the thyroid there was, 
with one exception, a uniform increase in physiological activity, as 
shown by the increased susceptibility to morphine. 
The changes in weight were in most cases not marked; in two 
instances there was a slight increase. The most marked change was 
with the mice of group C; the average loss of weight with these was 
18 per cent. Perhaps this indicates that the mice of this series had 
eaten more of the cakes than had the mice of the other series. 
The following series may be quoted as additional illustrations of 
how the susceptibility of mice to morphine may be increased by the 
administration of thyroid : 
SERIES IV. 
Gm. thy- 
roid fed 
Percentage 
of iodine 
Mg. I in 
thyroid 
Fatal dose in mgm. 
per gm. 
Loss in 
weight.a 
daily. 
in thyroid. 
fed daily. 
Recovered. 
Died. 
A 
B. Controls 
0. 01 
0. 19 
0.019 
0.10 , 
.36 I 
0. 15 ! 
5.1 
+6.8 
SERIES 
V. 
A 
B. Controls 
0.03 
0.186 
0.0558 
0.18 1 
.38 
0.22 
.43 
14.2 
7.9 
SERIES 
VI.o 
1 
A 
B. Controls 
0.2 
0. 186 
0. 0372 
0.07 
.24 
0.08 
.24 
1.9 
1.5 
a The + sign indicates that the mice had. increased in weight. 
b The experiment was continued, but six days instead of ten, as was usually the case. 
SUMMARY OF EXPERIMENTS OX MICE. 
The above experiments show that the resistance of mice to mor- 
phine was uniformly lowered by the feeding of thyroid. This lower- 
ing of the resistance occurred independently of the changes in weight ; 
in some cases there was a markedly increased susceptibility to 
morphine with an increase in weight. In general the thyroid con- 
taining the higher percentages of iodine caused the greatest changes 
in resistance, but there were a number of exceptions. 
c. — E xperiments on Guinea Pigs. 
. Experiments were, not made in which the effects of thyroid con- 
taining different percentages of iodine upon the resistance of guinea 
pigs to morphine were determined. The following experiments show 
that the resistance of these animals to morphine is di m i n ished by the 
feeding of thyroid. The amount of thyroid was very large; in the 
