OF THE HAIRS. 17 1 



they very slowly become coloured, so that in youth they are, iu 

 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 pubis. 



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 per- 

 fectly, that they remain permanently only T \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 contains much or little 

 moisture. They become longer or shorter, according to the 

 amount of moisture which they contain, whence their use in 

 Hygrometry. In spite of their extensibility, their strength is 

 considerable, and hairs of the head will bear at least 6 ounces 

 without breaking. 



lite chemical composition of the hairs is not yet sufficiently 

 understood, 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 decomposition. 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 consti- 

 tuents, 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 putrefaction better than any other part of the 

 body, so that even mummy hairs are found to be quite un- 

 changed; in water they are not dissolved, except in Papui's 

 digester. Metallic oxides colour 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 pro- 



