Chinese Journal of Physiology

THYROID AND HAIR GROWTH 67

SUMMARY

1. Partial feeding or starvation retards hair growth, but if thyroid is given in proper amounts, the hair may grow at nearly normal rates. Ixcess of thyroid depresses hair growth.

2. Since thyroidectomy also retards hair growth, while undernutrition causes regression of the thyroid gland, the thyroid secretion may be considered to be the most important factor controlling the growth of hair.

3. The optimal dose of thyroid is between 0.6 and ().7 gm, larger

doses depress hair growth.

+, It is suggested that the cause of the variation in hair growth rate in normal animals is variation in the individual level of thyroid secretion.

5. Iodine, tyrosine and tryptophane cannot replace thyroid.

6. Sex has no influence, but age has. The rate of hair growth is slower before 71 days than after, when it is relatively constant.

7. When thyroid is given the hair tends to become more glossy and to fall out more readily.

\We are indebted to Dr. E, Tso for a supply of some of the experimental animals.

LITERATURE ].. CHaNe, H. C. Am. J. Physiol., 1925, 73, 275-286, 2. Crane, H. C. Am, J. Physiol., 1926, 77, 562-567, 3. Coxtins, H. H. J. Exper. Zool,, 1918, 27, 73-99, 4, Scuurtz, W. Arch, f, Entwg., 1916, 42, 222-242, 5. Trorrer, M, Anat, Rec., 1928, 87, 878-379.