No attempt will be made in this article to give a comprehensive review of the literature, as this has been done most extensively by Boothby in 1921, Biedl in 1922, Carlson in 1924, Dragstadt in 1927, and many other writers, but I will mention a few of the more salient points. Symptoms of tetany following complete or partial thyroidectomy has been an exasperating complication of the surgical treatment of goiter. In the early surgery of the thyroid the anatomy and physiology of the thyroid and parathyroid glands were not well known, and thyroid and parathyroid deficiency were confused. There are usually four parathyroid glands, each about 6 by 4 by 2 millimeters in size, the two superior glands being most constantly placed. They are more often found in the angle between the trachea and esophagus on the level with the cricoid cartilage, usually embedded in the meshes of the pretracheal fascia. The two inferior glands maintain a position ranging from the level of the lower third of the thyroid gland to the mediastinum. McCullom states that the two superior glands are never placed within the true capsule of the thyroid. The subtilty of the parathyroid glands has rendered them the subject of much study and research. Sandstrom, in 1880, was the first to describe their microscopical structure, though these bodies had been previously observed by Remak and Virchow. Sandstrom at that time thought them to be undeveloped thyroid tissue, and credited them with no special physiological function. Gley, in 1891, after reviewing three hundred cases, observed that death following thyroidectomy was due in many cases to tetany. He seemed of the opinion that the tetany was due to a disturbance of the “Thyroides Surnumeriaises.” Vassole and Generali, in 1896, demonstrated that the tetany was due to a disturbance of the parathyroid function. MacCallum and Vogel, in 1913, expressed the opinion that the blood of animals during tetany contained something which rendered the nervous system more irritable; during the same year they found the blood of these animals to be deficient in calcium. Macf.allum had previously (in 1908) discovered that administering calcium lactate allayed the symptoms of tetany. A number of investigators experimented with extracts of the parathyroids, with little success. It remained for Collip, in 1925, to discover the parathyroid autocoid which is capable of preventing or controlling the symptoms of parathyroid hypofunction. It is also capable of restoring to normal level the blood calcium of animals with hypocalcemia. It is well established that the parathyroids have a special physiological function, and are instrumental in maintaining a normal calcemia. Kocher for a time enucleated the thyroid gland when treating goiter surgically. Tetany ensuing in a high percentage of these cases, this pioneer of thyroid surgery in 1881 discontinued the complete removal of the gland.