386 EXCRETION. 



The second variety, the short, stiff hairs, is found at the entrance of the nostrils, 

 upon the edges of the eyelids, and upon the eyebrows. 



The third variety, the short, soft, downy hairs, are found on the general surface 

 not occupied by the long hairs, and in the caruncula lachryraalis. In early life, and ordi- 

 narily in the female at all ages, the trunk and extremities are covered with downy 

 hairs ; but, in the adult male, these frequently become developed into long, soft hairs. 



The hairs are usually set obliquely in the skin and take a definite direction as they 

 lie upon the surface. Upon the head and face, and, indeed, the entire surface of the 

 body, the general course of the hairs may be followed out, and they present currents 

 or sweeps that have nearly always the same direction. 



The diameter and length of the hairs are exceedingly variable in different persons, 

 especially in the long, soft hairs of the head and beard. It may be stated in gen- 

 eral 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 hairs of the head measure 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 terminate in pointed extremities ; and sometimes in hairs that have been cut, the 

 ends become somewhat pointed, although they are never so sharp as in the new hairs. 



Of the long hairs, the finest are upon the head, where they average about ^^ of 

 an inch in diameter, the extremes being from 15 1 06 to T ^g- of an inch for the finest, 

 and from ^$ to yi-^ of an inch for the coarsest. The hair is ordinarily coarser in 

 women than in men. Dark hair is generally coarser than light hair ; and, upon the 

 same head, the extremes of variation are sometimes observed. The hairs of the beard 

 and the long hairs of the body are coarser than the hairs of the head. Wilson esti- 

 mates that the average 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 f^ to -^ of an inch in diameter, and the fine, downy 

 hairs, from ^^-g- to T^OTT of an inch. The variations in the color of the hairs in different 

 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 

 varies with their thickness, but an ordinary hair from the head will bear a weight of 

 six or seven ounces. A well-known property of the hair is that of becoming strongly 

 electric by friction ; and this is particularly well-marked when the weather is cold and 

 dry. The electricity thus excited is negative. Sections of the shaft of the hairs show 

 that they are oval, but their shape is very variable, straight hairs being nearly round, 

 while curled hairs are quite flat. Another peculiarity of the hairs is that they are 

 strongly hygrometric. They readily absorb moisture and become sensibly elongated, a 

 property which has been made use of by physicists in the construction of delicate hy- 

 grometers. 



Boots of the Hairs and Hair-follicles. The roots of the hairs are embedded in fol- 

 licular openings in the skin, which differ in the different varieties only in the depth to 

 which they penetrate the cutaneous structure. In the downy hairs, the roots pass only 

 into the superficial layers of the true skin ; but, in the thicker hairs, the roots pass 

 through the skin and penetrate the subcutaneous cellulo- adipose tissue. 



The root of the hair is softer, rounder, and a little larger than the shaft. It be- 

 comes enlarged into a rounded bulb at the bottom of the follicle and rests upon a fungi- 

 form papilla, constricted at its base, to which it is closely attached. In describing the 

 connection between the hairs and the skin, anatomists mention three membranes forming 

 the walls of the hair-follicles, and two membranes that envelop the roots of the hair in 



