THE HAIR, 



253 



bed closely filled with fat-granules of various sizes. It is an inte- 

 resting fact, and not well explained, that the nails become deformed 

 (curved toward the free edge), in phthisis and cyanosis. In the 

 rabbit, it was found by Steinruck that the division of the ischiatic 

 nerve caused the nails and hair to fall off. 



Fig. 159. 



SECTION III. 

 THE HAIE. 



Each hair consists of its shaft (scapus), and the root ; the former 

 including all that projects free from the surface of the skin ; the 

 latter, the portion beneath the surface. 

 (Fig. 159.) The bulb is the deepest 

 portion of the root, and is from 1J to 

 3 times the diameter of the shaft. 



A. The shaft in straight hairs is 

 rounded and straight; undulated and 

 flattened in the wavy; and spirally 

 twisted and flat, or slightly ribbed, in 

 curly and woolly h'airs. It consists of 

 1, the cortical or fibrous substance, 2, 

 the cuticle, and 3, the medulla, which 

 is, however, often absent. 



1. The fibrous substance, which con- 

 stitutes the greater part of the bulk of 

 the hair, is striated longitudinally, 

 streaked or spotted, and more or less 

 colored, except in white hairs, in which 

 it is transparent. The color is some- 

 times pretty regularly distributed 

 through its whole substance ; at others, 

 concentrated in a few elongated granu- 

 lar spots. By the action of hot con- 

 centrated sulphuric acid, the fibrous 

 portion of the hair is shown to be 

 made up of flat, elongated fibres of 



Various breadths (goVu ^O Z^GU f an root - sheatl1 - 9- Basement-membrane of 



inch), of marked rigidity and brittle- *^2^$Z 



ness, and with notched margins and * Excretory duct of sebaceous glands, 



ends. In dark hairs, they have a dark ^S^^SSm &ST, 



tinge ; in pale ones they are clear. the skin - n - Cuticle of do. somewhat re- 



m-i rt-i , -i 11- traded into the sac. o. Outer root-sheath. 



These fibres are not, however, the ulti- -Magnified soo diameters, 



