180 SPECIAL HISTOLOGY. 



never failed to find it always beautifully distinct. In rare 

 cases the medullary tract is double throughout (Bruns, figure 

 in Hassall), more frequently divided in places into two tracts, 

 which soon unite again. In the lower part of the root, the 

 medulla, which is here clear, is often thicker, and exhibits 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 originally 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 papilla 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, subsequently drying up ; but in these instances, ac- 

 cording to Brocker, it never, even after the action of potass, 

 exhibits a cellular texture, whilst this is alwavs 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 numerous dark, reticulated, irregular or even 

 jagged lines, which surround the hair at intervals of 0-002 — 

 0006'" from one another, and occasionally 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 trans- 



