94 
Moreover, the evidence is far from conclusive that there may not 
have been differences between the two thyroid preparations other 
than that of the iodine content. There is also the possibility to be 
considered that the potassium iodide that was administered during 
the course of eighteen days had in some way simply stimulated the 
thyroid to an increased production of an active substance and that 
this active substance secondarily retained an additional amount of 
iodine and that the increased activity of the gland was due to the 
former and not to the latter. 
It seemed to us that the following conditions should be fulfilled in 
order to make an experiment of this character conclusive: There 
should be evidence that the thyroid of the animals which received 
the iodine compound was, before its administration, in approximately 
the same condition as those which were to serve as controls; and, in 
the second place, the iodine should be administered for but a short 
time, so as to exclude any prolonged stimulating action. We endeav- 
ored to meet these conditions as follows: The thyroids of several 
groups of ten dogs each were analyzed for iodine, so as to obtain data 
as to the usual percentage of iodine present. To similar groups of 
ten dogs two doses of potassium iodide or of iodoform were given on 
successive days and the dogs killed on the third or fourth day. It 
was found that a large amount of iodine was taken up by the thyroid 
and that the latter, tested by our methods, showed greatly increased 
activity. Moreover, the increased activity was in direct proportion 
to the amount of iodine which had been taken up by the thyroid. 
We believe the conclusion is justified that the physiological activity 
of the thyroid from the different groups of dogs was approximately 
the same before the iodine was given, and therefore the increased 
activity of the thyroid of the iodine-fed dogs must have been due 
entirely to the iodine absorbed. The increased activity appeared 
much too rapidly to permit of the supposition that the iodine had 
simply accelerated the production of a more powerful substance 
independent of the iodine. The experiments were as follows: 
SERIES A. 
Forty-six dogs were divided into five groups. There were ten 
animals in each of the first three groups, seven in the fourth, and 
nine in the fifth. To each of the dogs of the fourth group from 1.5 
to 2 grams of potassium iodide were given per os; they were killed 
twenty-four hours later. Each of the dogs of the fifth group received 
1 to 1.3 grams iodoform in capsules; this was repeated on the fol- 
lowing day and the dogs killed on the third day. The thyroids from 
all these dogs were weighed, ground up finely, dried at 50° C. and 
again weighed, and the iodine determined. 
