In the majority of cases the tumour in the neck develops slowly, and does not reach its full dimensions until after middle life. Goitre in this form, although inconvenient, causes no serious discomfort. But when it appears in early life, it is associated with an extraordinary complex of malformations and ill-performed functions. The condition into which a goitrous child sinks is known as cretinism. With the exception of the skull-case, its skeleton does not attain to its proper proportions; and, since the soft parts do not equally submit to arrest of growth, the dwarf is heavy and ungainly, with large jowl and protuberant abdomen. The appearance of distortion is extraordinarily heightened by hypertrophy of the skin and the subcutaneous connective tissue. Ears, eyelids, nose, lips, fingers, are thick and heavy. The hair and nails are coarse. The skin is folded, wrinkled, rough. The bodily ungainliness of a cretin has its counterpart in the deformity of his mind. He is an idiot whose deficiency is chiefly marked by apathy. Cretinism exhibits itself in varying degrees. The description that we have just given would not be accurate for all. For the sake of brevity, we have chosen a case which might be that of a goitrous cretin of a certain type, or that of a cretin whose thyroid gland, in lieu of showing what looks like overgrowth, has failed to properly develop. Nothing is more remarkable with regard to this organ than the fact that the condition associated with its overgrowth and the effects of its atrophy, or inadequate growth, are the same. A consideration of the function of the gland will suggest an explanation of this seeming paradox. The inconvenience caused by goitre induced surgeons, about twenty-five years ago, to remove the tumour in simple uncomplicated cases. Owing to the accessibility of the gland, the operation is both safe and easy; but its removal was found to be followed by symptoms of a very serious nature, especially overgrowth and œdema of subcutaneous tissue, muscular twitchings and convulsions, mental dulness. About the same date, physicians recognized that the disease myxœdema—so called because the œdema is not watery, as in dropsy, but firm and jelly-like—is due to deficiency of the thyroid gland.