THE HAIE. 255 



^J^ to T^fltf of an inch wide. Yery similar appearances are, how- 

 ever, sometimes produced by the boundary lines of the hair-plates. 



This description of the fibrous substance of the shaft applies 

 also to that portion of the root which is solid and brittle. In the 

 deeper and softer portions, the hair-plates are less rigid and have 

 the form of more or less elongated cells with cylindrical, straight, 

 or serpentine nuclei, easily rendered apparent by acetic acid. Fi- 

 nally, in the bulb they are merely round cells 4^^ to 5^0^ of an 

 inch in diameter ; closely packed together, and, like the Malpighian 

 layer of the epidermis, sometimes containing colorless granules, and 

 sometimes so full of colored ones as to constitute true pigment-cells 

 in appearance. 



The color of the fibrous portion of the hair is due partly to 

 granules of pigment, to some extent to the air-cavities, and partly 

 to a pigment blended with the substance of the hair-plates. The 

 granule-pigment presents all shades, from clear yellow through 

 red and brown to black. The last mentioned, or diffused pigment, 

 is quite absent in white hairs, and is scanty in clear fair hairs. It 

 is most abundant in the more opaque fair hairs, and in red as well as 

 in dark hairs; it alone sometimes producing an intense red or brown 

 color. These two pigments vary in their proportion ; but are about 

 equal in very light and in very dark hairs. 



2. The cuticle of the hair is a very thin, transparent pellicle in- 

 vesting the hair, and in intimate union with the fibrous substance. 

 It consists of but a single layer, composed of plates arranged like 

 tiles; and is g^ to ^^ of an inch thick. Each plate is gj<j to 

 7 Js of an inch in the transverse direction of the hair, and 7$^ to 

 gJo in that of its length (Fig. 161, c?, c?'); and is only about 27333 

 of an inch thick. On the lower part of the root, however, there 

 are two layers of epidermis. (Fig. 162, c, d.) The cells of the outer 

 layer are thicker than those of the inner, its whole thickness here 

 being ^<j<j to g^ of an inch; while the inner is ?B > CT , to ^fa of 

 an inch thick. Kolliker states that the two layers of epidermis pass 

 into the outer nucleated cells of the bulb. 



3. The medullary substance varies most of all of the constituents 

 of the hair. It is a cord extending in the axis of the hair from 

 near the bulb almost to the point. It is usually present in the thick, 

 short hairs, and the stronger long ones, and the white hairs of the 

 head; and absent in the down (lanugo) and the colored hairs of the 

 head. It consists of from one to five columns of superimposed cells, 



