We know that certain drugs, as found by Garnier, have an exciting action upon the thyroid, such as iodine, and what is especially important, pilocarpine. The great sudorific action of this drug may stand in some relation to its effect upon the thyroid. It is permissible to suppose that the different drugs which antagonize fever do so by acting first upon the thyroid gland and exciting its increased activity to fight infection. But if we gave too much of these we might exhaust the activity of the gland in the same way as Garnier found an exhaustion of the colloid of the thyroid after too much iodine. This shows that we should not give antipyretics in too large doses. We should excite thyroid activity but not overdo it. That the thyroid is able to protect us against infectious diseases can be best shown by the fact that it exercises a great influence upon phagocytosis. According to the findings of Fassin, the alexins disappear from the blood after the extirpation of the thyroid gland; and, according to Sir Almroth Wright, the production of opsonins is dependent upon internal secretions. Hence, it is of the greatest value to us that Stepanoff[72], and Marbé have proved by experiments conducted in the Pasteur Institute of Paris that the opsonins disappear after the extirpation of the thyroid gland but increase after thyroid treatment, these experiments thus proving the correctness of our clinical observations on the rôle of the thyroid gland as an organ for protection against infections, as published in _The Lancet_ two and one-half years ago. Sajous, who was first (1907) to point out that the thyroid secretion was the agent which Wright termed “opsonin,” is also shown to have been right by the investigations of Fassin, Stepanoff and Marbé, thus proving further the intimate relationship between the thyroid and our immunizing functions. Footnote 72: Stepanoff: Comptes Rendus de la S. B. de Paris, 1908.