172 SPECIAL HISTOLOGY. 



the caruncula lachrymalis, and those (frequently absent) of the labia 

 minora (Henle). 



The number of hairs upon a given extent of surface varies very n>uch, 

 depending especially upon age, sex, and the color of the hairs. Accord- 

 ing to Withof, on a surface of J of a square inch there were found 147 

 black, 162 brown, 182 fair hairs. In a moderately hairy man, he found 

 on ^ of a square inch, 293 upon the scalp, 39 on the chin, 34 on the 

 pubis, 23 on the fore arm, 19 upon the outer margin of the back of the 

 hand, 13 on the anterior surface of the leg. In men, closely set hairs 

 occur not unfrequently upon the chests, shoulders, and extremities. 



The hairs are placed either singly, or in twos and threes, even four and 

 five together. The latter is the rule in the foetus, but the same disposi- 

 tion obtains also in adults, especially in the lanugo. As Osiander and 

 especially Eschricht, have shown, the direction of the hairs and hair-sacs 

 is rarely straight, but oblique, and in different degrees in different parts 

 of the body, as may be demonstrated with ease in the hairs of embryos, 

 and, though less obviously, in adults also. The regularity depends on this, 

 that the hairs being arranged in curved lines, which converge towards 

 either certain points or certain lines, or diverge from them in two or more 

 directions; there result a multitude of figures, which may with Eschricht 

 be denominated " streams," " whorls," and "crosses." Streams with 

 converging hairs are found, for example, in the median line of the back, 

 chest, and abdomen, in the line which answers to the ridge of the tibia, 

 &c. &c. ; streams with diverging hairs occur on the line between the 

 thorax and abdomen, on the one hand, and the back on the other, &c. ; 

 whorls and crosses Avith diverging hairs are found in the axilla, on the 

 scalp, at the internal angle of the eye ; with converging hairs, on the 

 elbow. For further details I must refer to Eschricht's figures and 

 descriptions, concerning which, however, it is to be remarked, that many 

 variations occur with regard to these points, and Eschricht's figures re- 

 present only some of them. 



§ 55. External peculiarities and chemical composition of the Hairs. — 

 In embryos, the hairs are generally quite colorless and clear ; they very 

 slowly become colored, so that in youth they are, in general, paler than 

 in middle age. In the adult the downy hairs, which have remained in 

 a foetal condition as it were, are invariably the palest ; the longer ones 

 are always darker, and the darkest are those of the head, beard, and 

 puhis. 



The hairs are very elastic ; according to Weber, they stretch without 

 breaking to nearly a third more than their length, and if they be 

 stretched only a fifth, they contract again so perfectly, that they remain 

 permanently only -j^i^th longer. They readily imbibe water, and as 

 readily give it out again ; they are therefore sometimes dry and brittle, 

 sometimes moist and soft, according as the skin or the atmosphere con- 



