130 



SENSE OF TOUCH. 



the tufts of hair on various parts cannot, in any way, be assimilated to 

 the hairy coating that envelopes the bodies of animals ; and is, in them, 

 manifestly intended as a protection against cold. 



Fig. 46. 



There is another class of bodies connected with the skin, and ana- 

 logous in nature to the last described, the 

 nails. These serve a useful purpose in touch, 

 and consequently require notice here. In 

 the system of De Blainville, they constitute 

 a subdivision of the hairs, which he dis- 

 tinguishes into simple and compound, 

 simple, when each bulb is separated, and 

 has a distinct hair; compound, when seve- 

 ral pileous bulbs are agglomerated, so that 

 the different hairs, as they are formed, are 

 cemented together to constitute a solid body 

 of greater or less size, nail, scale, horn, 



Section of the Skin on the end of &c ** , man > the nail alone exists ; the chief 

 the Finger. and obvious use ot which is to support the 



The cuticle and nail, n, detached pulp of the finger, whilst it is exercising 



from the cutis and matrix, m. touch. Animals are provided with horns, 



beaks, hoofs, nails, spurs, scales, &c. All 



these, like the hair, grow from roots ; and are considered to be analogous 

 in their physical and vital properties. Meckel, and De Blainville, 

 Bonn, Walther, Lavagna, and others, are of opinion, that the teeth are 

 of the same class ; and that they belong, originally, to the skin of the 

 mouth. 



The nails, near their origin, are seen, under the microscope, to con- 

 sist of primary cells, almost identical with those of the epidermis; these 

 gradually dry into scales; and the growth of the nail appears to be 

 effected by the constant generation of cells at its root and under sur- 

 face; and as successive layers are pushed forward, each cell becomes 

 larger, flatter, and drier, and more firmly fixed than those around it. 1 

 The chemical composition of the epidermis and the nails is similar to 

 that of the hair: yet according to Mulder, 2 there are material differ- 

 ences in their properties ; the latter, being almost insoluble in strong 

 acetic acid, in which the other two are readily soluble : hence he infers 

 the composition of hair and of horn and whalebone must differ materi- 

 ally; and, that, accordingly, Scherer's conclusion, that they are all 

 identical is incorrect. The following are the results of the analysis of 

 each of these bodies. 



C. 



H. 

 N. 

 O. 



s. 



Epidermis. 



50.28 



6.76 



17.21 



25.01 



0.74 



Horn. 

 51.03 



6.80 

 16.24 

 22.51 



3.42 



Whalebone. 

 51.86 



6.87 

 15.70 

 21.97 



3.60 



Hair. 



50.65 



6.36 



17.14 



20.85 



5.00 



For physiological purposes, the above description is sufficient. A few 



' Henle, edit, cit., i. 289, Paris, 1843. 



9 The Chemistry of Vegetable and Animal Physiology, translated by Fromberg, p. 527. 

 Edinb. and London, 1849. 



