It appears to have become established by recent observations that there is danger in certain parts of the United States and elsewhere, of human beings and animals failing to secure in their food a sufficient amount of iodin. This element is present in the thyroid gland to the extent of about 0.2 per cent of the dried weight of the gland, or about 10 to 15 mgms. in the entire gland. This element is essential for the formation of an organic iodin-containing compound which acts as a hormone or regulator of metabolism. Kendall (11) has isolated this substance from the thyroid glands of animals and has given it the name thyroxin. A lack of iodin in the diet prevents the formation of this hormone and leads to hyperplasia and enlargement of the gland.

Goiter is very common around the Great Lakes, in the upper Missouri and Yellowstone valleys, in Eastern Oregon and Washington, and has been attributed to lack of iodin in the soil and water of those regions.

Salmon and trout, which are reared under hatchery conditions and fed liver and are crowded, and kept in water which is not changed frequently enough, have suffered greatly from goiter. It has been shown by Marine, Lenhart and others (12) that treatment of the water in which the fish are kept, with potassium iodid, causes retrogression of the thyroid and a return to normal. Feeding the fish upon hashed sea-fish also led to improvement in the condition of their thyroids, presumably because sea-fish contain iodin. Wild fish do not suffer from this disease. Pike and bass in Lake Erie frequently suffer from goiter (13).

In the Yellowstone river valley there has been for some time a loss of approximately one million young pigs and numerous lambs, calves and colts each year as the result of thyroid disease. This most serious problem in animal production has been studied by Smith (14), who found that it was only necessary to administer sodium or potassium iodid to the pregnant sows in order to prevent the condition. As the result of the shortage of iodin many of the pigs were born dead, others died within an hour or two while still others lived twenty-four to thirty-six hours. These pigs were born in a hairless condition, and with great enlargement of the thyroid gland.

Hart and Steenbock (15) have reported results with pigs which are confirmatory of those of Smith.

Marine and Kimball (16) studied the effects of administering sodium iodid to girls in the public schools of Akron, Ohio, on the incidence and course of goiters among them. In a complete census of the condition of the thyroid gland in the girls from the fifth to the twelfth grades of the school population in this goiter-ous district, it was found that 1,688 or 43.59 per cent had normal thyroids; 2,184 or 56.41 per cent had enlarged thyroids, and 594 or 13.4 per cent had well-defined, persistent thyroglossal stalks.

They administered sodium iodid to a large number of these girls, and six months later a reexamination of their thyroids was made. The following table shows the results and also the data secured with another group of girls who did not take the prophylactic treatment.

These results indicate clearly the value of the administration of suitable doses of iodids at intervals, as a means of preventing the hyperplasia of the thyroid gland.