OF THE NAILS. 



163 



transverse sections (Figs. 58, 61), as pointed processes of 0-01-0-02 of 

 a line in length, which, as a rule, are most strongly developed at the 

 edges of the nail, even to 0-04-0-06 of a line, and answer precisely in 

 their number to the laminae of the under side of the stratum Malpiyliii. 

 The upper surface of the substance of the nail is smooth, taken as a 

 whole, yet sometimes even here, very distinct, parallel, longitudinal 

 streaks appear as the last, almost effaced indications, of the inequalities 

 of its bed. 



Usually, the thickness of this part of the nail continually increases 

 from the root to near the free edge, so that the body of the nail is, an- 

 teriorly, at least three times thicker (from 0'3 to 0-4 of a line) than the 

 former ; at the free edge again, it becomes somewhat less. In its trans- 

 verse diameter also, with the exception of the posterior edge of the root, 

 the substance of the nail is not everywhere equally thick ; it thins con- 

 siderably towards the lateral edges, so that at last the nails, where they 

 lie in the fold, measure not more than 0-06-0-12 of a line, and finally 

 terminate quite sharply. 



With regard to the structure of the proper substance of the nail, it 

 can hardly be made out without the action of reagents. In perpen- 

 dicular sections we see, particularly in the body, nothing but horizontal, 

 fine, straight, or curved, closely-approximated lines, which one would be 

 inclined to consider as the optical expression of delicate, superimposed 

 lamellae, and between these, a multitude of elongated, horizontal, 

 opaque or peculiar reddish-transparent striae, evidently nuclei. Only 

 upon the most posterior part of the root, and on the under surface, where 

 it meets the stratum Malpighii, do more or less distinctly flattened cells 

 with nuclei appear disposed in layers. Horizontal sections show even 

 less than the perpendicular ones ; exhibiting a pale transparent sub- 

 stance, granular here and there, and 

 mostly without indication of any 

 structure whatsoever, occasionally 

 with very indistinct contours of plates 

 similar to those of the horny layer of 

 the epidermis. Very different are 

 the appearances presented after 

 treating the nail with alkalies and 

 certain acids. 



If the substance of the nail be 

 boiled in dilute caustic soda, it be- 

 comes changed upon the first bub- 

 bling of the fluid into a beautiful 

 cellular tissue (Fig. 62, A, B\ whose 



Fi K . 02. 



FIG. 02. Nail plates boiled with caustic soda. 

 a, membranes of the distended elements of the nail ; 

 from the side. Magnified 350 diameters. 



A, from the side ; _B, from the surface : 

 , their nuclei, from the surface ; c, 



