Chap. XXV. COKEELATED VARIABILITY. 319 



tends to increase the growth of the hair, as is well shown in 

 the abnormal growth of hair near old inflamed surfaces. 

 Now, Professor Low 16 is convinced that with the different 

 races of British cattle thick skin and long hair depend on 

 the humidity of the climate which they inhabit. We can 

 thus see how a humid climate might act on the horns — in the 

 first place directly on the skin and hair, and secondly by 

 correlation on the horns. The presence or absence of horns^ 

 moreover, both in the case of sheep and cattle, acts, as will 

 presently be shown, by some sort of correlation on the skull. 

 With respect to hair and teeth, Mr. Yarrell 17 found many 

 of the teeth deficient in three hairless " Egyptian dogs," and 

 in a hairless terrier. The incisors, canines, and the premolars 

 suffered most, but in one case all the teeth, except the large 

 tubercular molar on each side, were deficient. With man 

 several striking cases have been recorded 18 of inherited bald- 

 ness with inherited deficiency, either complete or partial, of 

 the teeth. I may give an analogous case, communicated to me 

 by Mr. W. Wedderburn, of a Hindoo family in Scinde, in which 

 ten men, in the course of four generations, were furnished, in 

 both jaws taken together, with only four small and weak 

 incisor teeth and with eight posterior molars. The men thus 

 affected have very little hair on the body, and become bald 

 early in life. They also suffer much during hot weather from 

 excessive dryness of the skin. It is remarkable that no 

 instance has occurred of a daughter being thus affected ; and 

 this fact reminds us how much more liable men are in England 

 to become bald than women. Though the daughters in the 

 above family are never affected, they transmit the tendency 

 to their sons ; and no case has occurred of a son transmitting 

 it to his sons. The affection thus appears only in alternate 

 generations, or after longer intervals. There is a similar con- 

 nection between hair and teeth, according to Mr. Sedgwick, 



16 'Domesticated Animals of the 17 ' Proceedings Zoolog. Soc.,' 1833 



British Islands,' pp. 307, 368. Dr. p. 113. 



Wilckens argues (' Landwirth. Wo- 18 Sedgwick, ' Brit, and F->rtign 



chenblatt,' Nr. 10, 1869) to the same M'dko-Chirurg. Review/ April, 1868, 



effect with respect to domestic animais p. 453. 

 in Germany. 



