In the other articles of this series, the function of the thyroid gland and its secretion has been presented in considerable detail. The points there brought out that are of paramount importance for the proper administration of thyroid preparations may be briefly restated here. The function of the thyroid gland is to furnish a secretion, the active principle of which is thyroxin. The exact physicochemical status of thyroxin as it leaves the thyroid gland is not known. Thyroxin is a catalyst that accelerates the rate of heat formation. In the normal person the quantity of thyroxin actively present in the cells of the body is probably between 8 and 14 mg., and the concentration of a healthy normal person apparently varies very slightly; that is, the concentration in the body is constant in the sense that the temperature, the alveolar carbon dioxid tension, etc., of the normal person are constant.
PLUMMER HS, BOOTHBY WM. GLANDULAR THERAPYTHE ADMINISTRATION OF THYROID PREPARATIONS. JAMA. 1924;83(17):1333-1335. doi:10.1001/jama.1924.26610170003017