Chinese Journal of Physiology

THYROID AND HAIR GROWTH 61

Thyroid. It has already been shown that thyroid improves the rate of hair growth in starved or underfed animals. When thyroid is given, the rate distribution of the underfed animals improves, when the comparisons are made on the basis of either the simultaneous controls, or the mean partial feeding rate. That is to say there are fewer below and more above the control or the mean rate.

Acceleration Simultaneous partial Retardation feeding rate

IV. Partial feeding 37 (7) 58 (11) 5 (1)

+thyroid

0.2—1.3 gm Mean partial feeding rate

Wie 5 58 (11) 37 (7) 5 (1) It must be noted, that the simultaneous controls are from periods of partial feeding (without thyroid) and not normal feeding. If the hair growth rates (IV) are compared with the rates obtaining during normal feeding, the distribution is intermediate between that of normal feeding and partial feeding, viz. Acceleration Mean normal rate Retardation VI. Partial feeding 11 (2) AT (9) 42 (8) + thyroid 0.2—1.3 gm The point is made clearer when the mean rates alone are considered; under normal feeding the rate is 26 days, under partial feeding 41 days and under partial feeding plus thyroid, 80 days. Thyroid thus undoubtedly accelerates hair growth in a certain number of individuals but apparently does not entirely make good the nutritional deficiency. The question arises, why does thyroid not accelerate the hair growth of all individuals, and what is the effect of varying quantities of the hormone? We shall first consider the effect of thyroid on normally fed

animals. Acceleration Simultaneous normal Retardation feeding rate VII. Normal feeding 50 (9) 30 (7) 11 (2) + thyroid 0.2—1.3 gm

The above distribution, based on comparisons with the simultaneous control rates, shows that as far as individuals are concerned the majority are accelerated by thyroid. But as the mean hair growth rate of the controls of this series was somewhat higher than the mean for the entire