122 EXCRETION. 



The diameter and length of the hairs are exceedingly vari- 

 able in different persons, especially in the long, soft hairs of 

 the head and beard. It may be stated in general terms that 

 the long hairs attain the length of from twenty inches to 

 three feet in women, and considerably less in men. There 

 are instances, however, in women, in which the hair of the 

 head measures considerably more than three feet, but these 

 are quite unusual. Like the nails, the hair, when left ,to 

 itself, attains in three or four years a definite length, but 

 when it is habitually cut it grows constantly. The short, 

 stiff hairs are from one quarter to one half an inch in length. 

 The soft, downy hairs measure ordinarily from one twelfth 

 to one half an inch. Hairs that have never been cut ter- 

 minate in pointed extremities; and sometimes in hairs that 

 have been cut, the ends become somewhat pointed, though 

 they are never so sharp as in the new hairs. 



Of the long hairs, the finest are upon the head, where 

 they average about ^J-g- of an inch in diameter, the extremes 

 ordinarily being from -3-^5- to -g-J-g- of an inch for the finest, 

 and from ^J-g- to yj^ of an inch for the coarsest. The hair 

 is ordinarily coarser in women than in men. Dark hair is 

 ordinarily coarser than light hair ; and upon the same head 

 the extremes of variation are sometimes observed. 1 The 

 hairs of the beard and the long hairs of the body are coarser 

 than the hairs of the head. Wilson estimates that the aver- 

 age number of hairs upon a square inch of the scalp is about 

 1,000, and the number upon the entire head about 120,000. 



The short, stiff hairs are from -^-^ to yfg- of an inch in 

 diameter, and the fine, downy hairs from 2o ^ 00 to 1 / 00 of 

 an inch. The variations in the color of the hairs in differ- 

 ent races and in different individuals of the same race are 

 sufficiently familiar. 



When the hairs are in a perfectly normal condition, they 

 are very elastic, and may be stretched to from one fifth to 

 one third more than their original length. Their strength 



1 WILSON, op. cit., p. 84, et seq. 



