Investigation was made of the effect of hypophysectomy on the growth of hair of rats and compared with that of bone and tooth. To measure the rate of growth, the thallium acetate method was used for hair growth and lead acetate method for bone and tooth growth. The results obtained are as follow. 1) The sham-operation did not affect the bone growth of proximal tibia. But 9 days after hypophysectomy the cartilage became obviously narrow, and bone almost stopped growing. 2) Nine days after hypophysectomy the longitudinal growth of incisal dentin was inhibited by about 60%. Calcification was also inhibited, but one month after hypophysectomy, incisors, though extremely inhibited, still continued growing. 3) Hypophysectomy had almost no effect on the hair growth, although it showed a slight retardation in the hair eruption. The conclusion thus attained was that, under hypophysectomy, organs differ in the rate of growth according to their embryological origin, and the hair growth is no effect. Then it is suggested that the hair has the specific property.
