TISSUES OF THE BODY. 165 



100. 



The nails of the human being differ from the epidermis in their greater 

 hardness and solidity, but correspond very essentially with the latter in 

 their chemical relations. Like the scales of the cuticle, they yield on 

 treatment with alkalies keratin, already mentioned ( 94). 



Analyses of the substance of human nail-tissue have been frequently 

 made ; of those available we will only quote the following, from Scherer 

 and Mulder : 



Scherer. Mulder. 



C, . . 51-09 51-00 



H, . . 6-82 6-94 



N, . . 16-90 17-51 



( 2-80 



S, \ 

 0,J 



25 ' 19 ) 21-75 



According to these, the proportion of sulphur in the keratin of nail- 

 tissue appears more considerable than that of the epidermis, in which it 

 only amounts to 0'74 per cent. (p. 152). The proportion of mineral con- 

 stituents was found to be 1 per cent. 



The tissue of nail, like that of the cuticle, is nourished by the blood- 

 ve'ssels of the matrix and furrow, and shows, in our condition of culture, 

 a constant and tolerably lively growth, exceeding by far the loss of sub- 

 stance induced by the ceaseless wear and tear going on at the free edge. 

 It appears, however, that with those who do not pare their nails, as, for 

 instance, the Chinese, the growth of the former reaches a limit eventually, 

 for those talon-shaped nails, of about two inches in length, sometimes met 

 with, do not increase any more, according to Hamilton. According to E. 

 H. Weber > the free edge is cast off at times in children in the form of a 

 crescentic strip. Some interesting experiments were made by JBerthold 

 in regard to the amount of growth of the nail, or, what is the same thing, 

 into the length of existence of a horny cell of the latter. Eegeneration 

 takes place, according to this observer, more rapidly in infancy than at 

 an advanced age, and in summer than in. winter; a nail, which requires 

 during the warm part of the year 116 days for its complete renovation, 

 consuming 152 days in the latter process during the winter. The nails 

 also of different fingers, as well as those of corresponding members on the 

 right and left hands, are said to be dissimilar in growth also. 



The mode in which they grow is as follows : The deeper cells of the rete 

 Malpighii preserve their position, whilst the horny lamina is pushed for- 

 ward over the softer layer of cells covered by it, by the constant production 

 of new elements at the posterior border of the root, which become trans- 

 formed into scales. That the nail anteriorly is considerably thicker than 

 behind is explained by ther fact that the more superficial cells of the rete 

 mucosum are also transformed on the surface of the matrix into horny 

 laminae, which unite with the under surface of the completed corneous 

 portion of the nail, strengthening the latter, and naturally pressed for- 

 ward with it. 



Now, just as there is a normal physiological renovation of the nail, so 

 do we find that the latter may be completely regenerated after having been 

 lost in an abnormal manner, provided that the matrix have preserved its 

 integrity. If the latter have suffered, an ill-formed nail is produced. 



And further, in that the nail is dependent for its growth on the vessels 

 of the matrix, it is easy to conceive how many affections combined with 



