Struck by the similarity of the effects of iodin and thyroid in the treatment of goiter, Kocher, in 1895, suggested the desirability of examining the thyroid for iodin, but the tests made in Berne were negative. In the same year, however, Baumann, in Freiburg, discovered the presence of iodin in no inconsiderable amounts in the thyroid of man and other animals, but even now, over thirteen years later, we are still uncertain as to just what part the iodin plays in the physiologic activity and the therapeutic effects of the thyroid. Baumann, and Boos who first studied the action of the iodin-containing constituent of the thyroid, were of the opinion that the iodothyrin was the active principle of the thyroid gland, but there were many who did not accept this view and looked on the iodin as merely an injurious substance which the thyroid had removed from the circulating blood.