The accessibility of the thyroid gland in the neck, the ease of surgical approach, the definite effects following its removal, and then the miraculous marvels of the feeding of thyroid have rendered it the centre of attack by the largest army of endocrine investigators. As a result we know more about the thyroid in childhood, adolescence, adult life and old age than about the other glands. In childhood, the subthyroid or thyroid deficient, the cretinoid type, the type resembling the cretin, is fairly common. The peasant's face, with the broad nose and the tough skin, coarse straight hair, the undergrowth, physical and mental, a persistent babyishness and a retardation of self-control development, make up the picture. He needs an excess of sleep, sleeps heavily, needs sleep during the day, when awakened in the morning still feels tired, and rather dull and restless, dresses slowly, has to be coaxed or forced to dress, gets to school late nearly every morning, does badly at the school, reaction time, learning time and remembering time being prolonged as compared with the average, and is lazy at home lessons. He perspires little, even after exertion, yet fatigues easily, is subject to frequent colds, adenoids, tonsillitis, and acquires every disease of childhood that happens along. Adolescence, the coming of menstruation, the first blooming of youth is delayed in the subthyroid. The secondary sex traits as they develop tend to be incomplete and to mimic those of the opposite sex. Yet in adolescence too there may be a sudden change and reversal of the whole process, a jump from the subthyroid to the hyperthyroid state. So a girl who has been dull and lackadaisical, with no complexion and every prospect of evolution into a wall flower, may be transformed into a bright-eyed woman, generally nervous and restless, high colored, and possessed of a craving for continual activity and excitement. Skin, hair and teeth become of the thyroid dominant type. The heart palpitates under the slightest stimulus, she perspires almost annoyingly, heat and emotion are prostrating. If such a transfiguration does not occur, the effect of the reconstructions of puberty is to create a person with about the following characteristics. 1. Height below the average 2. Tendency to obesity (toward middle age) 3. Complexion sallow 4. Hair dry--hair line high 5. Eyebrows scanty, either as a whole or in outer half 6. Eyeballs deep-set, lack lustre, in narrowed slits 7. Teeth irregular, become carious early 8. Extremities cold and bluish 9. Circulation poor. Subject to chilblains