126 EXCRETION. 



the hair and the structure of its sheaths and the hair-follicle 

 are shown in Fig. 5. 



Structure of the Hairs. The different varieties of hairs 

 present certain peculiarities in their anatomy, but all of 

 them are composed of a fibrous structure forming the greater 

 part of their substance, covered by a thin layer of imbricated 

 cells. In the short, stiff hairs, and in the long, white hairs, 

 there is a distinct medullary substance ; but this is wanting 

 in the downy hairs, and is indistinct in many of the long, 

 dark hairs. 



The fibrous substance is composed of hard, elongated, 

 longitudinal fibres, which cannot be isolated without the aid 

 of reagents. They may be separated, however, by treating 

 with warm sulphuric acid ? when they present themselves in 

 the form 'of dark, irregular, spindle-shaped plates, from -^ 

 to -g^o- of an, inch long, and from - gT 1 TFF to g-^ of an inch 

 wide. These contain pigmentary matter of various shades, 

 occasional cavities filled with air, and a few nuclei. The 

 pigment may be of any color, from a light yellow to an in- 

 tense black, and it is this substance that gives to the hair 

 the great variety in color which is observed in different per- 

 sons. In the lower part of the root the fibres are much 

 shorter, and at the bulb become transformed, as it were, into 

 the soft, rounded cells found in this situation covering the 

 papilla. 



The epidermis of the hair is excessively thin, and is com- 

 posed of flattened, quadrangular plates, overlying each other 

 from below upward. These scales, or plates, are without 

 nuclei, and exist in a single layer over the shaft of the hair 

 and the upper part of its root ; but in the lower part of the 

 root the cells are thicker, softer, are frequently nucleated, 

 and exist in two layers. 



The medulla is found in the short, stiff hairs, and it is 

 often beautifully distinct in the long, white hairs of the head. 

 According to Sappey, it is found more or less distinctly 



