180 SPECIAL HISTOLOGY. 



the nuclei of its cells very distinctly, especially after the addition of 

 acetic acid. Steinlin and Eylandt assert of the medullary substance, 

 that it does not belong to the proper hair, but to its papilla, and origi- 

 nally represents a prolongation of this into the free part of the hair, 

 which then dries up. This is incorrect. The papilla or germ of the 

 hair is a part of the cutis, and has the same structure as the papillae, of 

 the latter, whilst the medulla of the hair is composed of isolated cells, 

 which by their resistance to alkalies, are in all respects allied to those 

 of the epidermis. On the other hand, in animals, as has long been 

 known, and as lately Brocker has especially shown, the papilla often 

 projects far, even to the point of the hairs, bristles or spines, subse- 

 quently drying up ; but in these instances, according to Brocker, it 

 never, even after the action of potass, exhibits a cellular texture, whilst 

 this is always obvious in the medullary substance, which is often present 

 at the same time. Such an elongation of the papillae may occasionally 

 be noticed even in man, to a certain extent ; thus Henle found it a few 

 times prolonged into a short point. But any prolongation of this kind 

 must be distinguished as decidedly from the cellular medullary substance, 

 as in animals. 



58. The cuticle of the Hair (cuticula\ is a very thin, transparent 

 pellicle, which completely invests the hair, and is very closely united 

 with the cortical substance. In its normal position, and observed in an 

 unaltered hair, it is evidenced by hardly anything more than by nume- 

 rous dark, reticulated, irregular or even jagged lines, which surround 

 the hair at intervals 0*002 0*006 of a line from one another, and occa- 

 sionally also by small serrations at its apparent edge (Fig. 70 A) ; if, 

 on the other hand, a hair be treated with alkalies, the cuticle is raised 

 in smaller or larger lamellae from the fibrous substance, and is even 

 separated into its elements. These are quadrangular or rectangular 

 flat plates without nuclei, generally pale and transparent (Fig. 70 B\ 



which do not swell up into vesi- 

 cles by the action of any re- 

 agent, and disposed in an im- 

 bricated manner, form a simple 

 membrane which completely 

 surrounds the cortex of the hair 

 in such a way, that the deeper 

 or lower cells cover the upper 

 ones. By sulphuric acid also 

 the structure of the epidermis is readily made out ; the hair is, as it were, 



Fia. 70. A, surface of the shaft of a white hair ; magnified 1GO diameters. The curved 

 lines mark the free edges of the epidermic plates: J5, epidermic plates from the surface, 

 isolated by the action of caustic soda ; magnified 350 diameters. One or both of their longer 

 edges are bent round, and so appear dark. 



