Chinese Journal of Physiology

58 H. C. CHANG anp T, P. FENG

Readings of the same side were usually compared. Milk and whole wheat flour constituted the control diet, fresh vegetable being given once a week. The general scheme of the experiment was as follows:. After the first control reading, say in a series of four animals, three were fed a limited portion of the normal or control diet, while one was continued | on the normal diet. Thyroid extract was given to one of the partial fed animals, iodine to the second and nothing to the third which served as a simultaneous control. Thus in each experiment, it was possible to compare the effect of thyroid (or iodine, etc.) with normal and partial feeding controls. The above scheme was more or less modified in different experiments according to the number of animals and substances tested. Besides thyroid siccum (Allen and Hanbury, and Armour) and iodine (Lugol’s solution), 1 per cent aqueous tryptophane solution (Pfanstiehl) and 0.25 per cent tyrosine in N/100 HCl were studied. The solutions were administered by drops: 2 or 3 for iodine, 3 for tryptophane and 14 for tyrosine per day. During intervals of rest between readings all the experimental animals were on full diet.

RESULTS

In judging the influence of our experimental procedures upon the rate of hair growth, no rate was considered abnormal unless the deviation from the control was greater than three times the mean error of the series. The rate is said to be accelerated when it is faster than the mean rate by 3 # and retarded when it is slower than the mean by the same margin (see table 1).

Regional difference. In many animals, readings were taken from both sides of the back. The rate of hair growth of the two sides may not be the same in individual cases, but when the entire series is analysed, the mean rate of hair growth is found to be about the same for both sides.

No. of observations Mean o #H Right side 96 30.7 12.6 1.3 Left ,, 100 28.8 10.6 1.6

Sex. No sexual difference in the rate of hair growth was observed in the present study (table 1 and fig. 1).