OF THE HAIRS. 173 



tains much or little moisture. They become longer or shorter, accord- 

 ing to the amount of moisture which they contain, whence their use in 

 Hygrometry. In spite of their extensibility, their strength is consider- 

 able, and hairs of the head will bear at least 6 ounces without breaking. 

 The chemical composition of the hairs is not yet sufficiently under- 

 stood, but they are chiefly composed of a nitrogenous substance, soluble 

 in alkalies with the evolution of ammonia, and insoluble in boiling acetic 

 acid. Scherer and Von Laer consider it to be a combination of protein 

 with sulphur, and the latter supposes, in addition, the existence of a 

 small quantity of a substance similar to gelatine, whilst Scherer regards 

 a second nitrogenous matter which he found, to be a product of decom- 

 position. Mulder considers the substance of the hairs to be a protein 

 compound combined with sulphamid, of which he finds 10 per cent. 

 Besides their nitrogenous constituents, the hairs, as even the earlier 

 investigations showed, contain a considerable quantity of dark or clear 

 fatty matter, which may be extracted by boiling in ether and alcohol. 

 From horn and epidermis, the substance of the hair is distinguished, 

 according to Mulder, especially by its insolubility in acetic acid and by 

 the same test, from albumen and fibrin. The hairs withstand putrefac- 

 tion better than any other part of the body, so that even mummy hairs 

 are found to be quite unchanged; in water they are not dissolved, except 

 in Papin's digester. Metallic oxides color the hair just as they do the 

 epidermis; thus, for example, they are blackened by the salts of silver 

 and manganese, sulphurets of these metals being produced. Chlorine 

 bleaches them. The ash amounts to about 1-2 per cent., and contains 

 oxide of iron (more in dark hair) ; oxide of manganese ; silica (traces) ; 

 phosphate of magnesia and sulphate of alumina were found by Jahn in 

 white hairs; and according to Laugin, copper occurs in the greenish 

 hairs of those who work in copper and brass. 



56. With regard to their more intimate structure, two substances 

 may be distinguished in all hairs without exception, and in many there 

 are three : 1, the cortical substance, or better, fibrous substance, which 

 constitutes by far the most considerable portion of the hair and deter- 

 mines its form ; 2, the cuticle, a delicate external investment of the 

 fibrous substance ; 3, lastly, the central medullary substance, which is 

 often absent. 



The cortical or fibrous substance is longitudinally striated, very often 

 presents dark dots, is streaked or spotted and except in white hairs, in 

 which it is transparent, is more or less deeply colored ; the color is 

 sometimes distributed through the whole substance with tolerable regu- 

 larity, sometimes more concentrated in certain elongated, granular spots. 

 The more intimate structure of the cortex of the hair, and the significa- 

 tion of its spots and striae, cannot be properly understood without the 

 use of acids and alkalies (which afford important aid in the investigation 



