Chinese Journal of Physiology

66 --H. C. CHANG ann T, P, FENG

General remarks.

In some animals, hair falls easily when thyroid medication has been well on the way. This type of hair falling is different from that of infectious origin. Thus in parasitic infections, the hair falls out in patches resulting in areas of alopecia. The hair coat is on the whole dry and brittle. On the other hand, during thyroid feeding, the hair seems to become less firmly rooted so that if the hairs are lightly touched, a number will fall out. This occurs in spite of the fact that the coating is moist and glossy, looking “‘better”’ than that of the normal animal. tno time is general or patchy alopecia observed following thyroid feeding. These observations point to an endogenous factor. Probably the metabolism of the hair follicles is disturbed, perhaps accelerated, so that the follicles are in an unstable condition.

When the whole dorsum of the animal is shaved, hair grows in patches of different pattern whose distribution varies in different shavings. When some areas (‘hair islands”) have attained full growth, no hair may appear in the intermediary regions. This phenomenon has been observed in the rabbit by Schultz (4) and in mice by Collins (8). Even in the small shaved square, irregularity in hair growth sometimes happens especially at one or other corner. For no apparent reason, in one corner of the shaved square the hair refuses to grow. It may be that this “corner defect’’ falls in the area between the “hair islands”. While poor regional blood supply may be the cause, the chance difference in the cyclic activity of the hair follicles, as pointed out by Trotter (5), may be another explanation. The latter is unlikely, however; as the chances of a defect occurring in the centre appears to be as good as the occurrence of a defect in the corner, yet a central defect is never observed. In the absence of any adequate explanation, all the readings complicated with the corner defect were discarded.

As noted before (2) and incidently mentioned above, the hair coating after thyroid medication becomes glosssy and soft. This happens frequently, and may or may not go together with acceleration of hair growth, indicating possibly a separate effect of thyroid. As it appears likely that the glossiness of the coat is related to the activity of the sebaceous glands, we are endeavouring to study the influence of thyroid on these structures, :