71 
activity was parallel to the iodine content. In the exceptional case 
the activity seemed to be somewhat less than was anticipated from 
the percentage of iodine; possibty the thyroid had been overheated 
in the process of drying or had undergone some decomposition, 
although there is little evidence that such treatment will materially 
reduce the activity of thyroid. 
Occasionally we encountered a series of experiments in which 
irregular results were obtained. In such cases the experiments 
were repeated at least twice and concordant results were obtained. 
The irregularities had probably resulted from some error in making 
the cakes or the amount of thyroid fed had been too large or too 
small to give results which could be compared, or perhaps the mice 
had not been kept under uniform conditions before the thyroid 
was fed. 
As pointed out elsewhere,® we have been able to foretell with con- 
siderable accuracy the iodine content of a thyroid preparation by 
comparing its physiological activity with that of another preparation 
the iodine content of which was known. 
Hi. EXPERIMENTS WITH THYROID FROM VARIOUS ANIMALS. 
One of the present writers 6 has shown in a previous publication 
that there is a parallelism between the amount of iodine and the 
physiological activity of the thyroid of a number of animals (guinea 
pig, cat, beef, sheep, hog, etc.). Thus a sample of hog thyroid with 
0.33 per cent iodine was about six times as active as one of guinea pig 
thyroid with 0.05 per cent; a sample of sheep thyroid with 0.176 
per cent was approximately three times as active as the guinea pig and 
but one-half as active as the hog thyroid, etc. 
We have been able to extend these observations to the thyroids of 
a large number of wild animals. 0 The results were similar, but the 
parallelism was not as strict as when thyroids of the same species 
were compared. The following illustrations may be given: The 
thyroid of a deer with 0.193 per cent iodine was about three times as 
active as that of a Barb ary sheep with 0.075 per cent; that of the 
Barbary sheep was more than twice as active as that of a sea lion 
with 0.022 per cent iodine. The thyroid of a cat with 0.08 per cent 
iodine was about as active as that of the Barbary sheep with 0.075 per 
cent, but it was distinctly more active than that of a dog with 0.111 
per cent. 
If we accept the view that iodine free thyreoglobulin has a low 
'degree of physiological activity, then such slight discrepancies may 
be explained on the supposition that different thyroids, with equal 
a R. Hunt and A. Seidell, J. Am. M. Ass., Chicago, 1908, 51, p. 1385. 
b R. Hunt, J. Am. M. Ass., Chicago, 1907, 49, p. 1324. 
c A few of these results were quoted on pp. 45 and 48. 
