SECT. 57-] HAIRS. 105 



arrangement in the foetus, but also occurs in the adult, especially 

 in downy hairs. As Osiander, and particularly Eschricht, have 

 proved, the direction of the hairs and hair-follicles is seldom 

 straight, but usually oblique j and is different in the various parts 

 of the body, which is easily shown in the hairs of the embryo, as 

 also in adults, although less distinctly. The regularity depends 

 upon this, that the hairs being arranged in curved lines, which 

 either converge towards fixed points or lines, or diverge from them 

 in two or several directions, a great number of figures arise, which 

 may, with Eschricht, be designated streams, whorls, and crosses. 

 Streams, with converging hairs, are met with in the mesial line of 

 the back, the chest, and the abdomen, and in the line over the ridge 

 of the shin-bone; streams with diverging hairs are found in the 

 lateral line, separating the abdomen and thorax from the back, etc. 

 "Whorls and crosses with diverging hairs occur in the armpit, ou 

 the crown of the head, the internal angles of the eyes, and with 

 converging hairs on the elbow. For more special details, I refer 

 to JEschricht's drawings and descriptions. 



§ 57. Physical Properties and Chemical Composition of the 

 Hairs. — The hairs are very elastic; they admit of being extended 

 nearly a third of their length, and when stretched only a fifth, 

 they contract again so completely, that they remain extended only 

 j'.th beyond their original length. They easily absorb water, and 

 as easily give it oft" again ; they are, accordingly, sometimes dry 

 and brittle, sometimes moist and soft, according as the skin or the 

 atmosphere contains much or little water. Their length alters 

 with their degree of moisture, upon which property their employ- 

 ment as hygrometers is founded. Their strength, notwithstanding 

 their extensibility, is considerable, and hairs of the head support 

 at least six ounces without breaking. 



The chemical composition of the h airs has not yet been sufficiently 

 elucidated. Their chief constituent is a nitrogenous substance 

 containing sulphur, which is soluble in alkalies with the develop- 

 ment of ammonia, but insoluble in boiling concentrated acetic 

 acid, and belongs to the albuminous class of compounds. The 

 hairs contain, according to their tint, a greater or less amount of 

 darker or lighter coloured fat, which can be extracted by boiling 

 in ether or alcohol. According to Mulder, they are distinguished 

 from horn and epidermis, especially by their insolubility in acetic 

 acid, and by the same character, also, from albumen and fibrine. 

 The hairs resist decomposition better than any other part of the 



