LESSON 26.J HAIR. 79 



each other, so that the whole surface of the barbs, of which the vane 

 consists, may form a solid, continuous, firm, resisting membranous 

 expansion, by which a feather strikes the air, as an oar strikes the 

 water. 



Were it not for this beautiful provision, the air would pass 

 through the feathers of the vane, and flight would be impossible. 



426. The cuticular substance of human hair, is composed of a 

 series of flatened cells or scales, derived from the epidermis thrown 

 off or exfoliated, from the interior of the follicle. These cells or 

 scales, are disposed in an imbricated (imbrex, a tile) FlG 

 form, or overlap each other, like the arrangement of 



shingles or tiles, on a nouse-top. This disposition of 

 the scales can be proved by a very simple experiment ; 

 place a hair between the thumb and finger, and pro- 

 ceed to spin it round, by moving the finger and 

 thumb contrary to each other ; the hair will inva- 

 riably pass through the root end first, which indi- 

 cates not only the imbricated arrangement of the E Human h 

 scales, but that they overlap from the root ; this is 

 shown in Fig. 118, the imbrications at the sides being exag- 

 gerated. 



427. As these scales are attached one by one, as they become 

 detached from the sides of the follicle, and the hair is always growing, 

 it follows that no two of them can be deposited exactly in the same 

 place consequently they overlap ; the lower part of a scale previ- 

 ously there, being covered by the upper part of a scale newly added. 



428. The cortical fibres of the shaft 

 of a hair are identical with the cells of 

 the bulb; they become elongated as 

 they are pushed upwards towards the 

 mouth of the follicle, by the production 

 of additional cells beneath, and are di- 

 minished in their diameter; consequent- 

 ly, the shaft of a hair is much less in diam- 

 eter than the bulb. 



. Epidermic scales of Human hair. 



429. The epidermic scales which cover 



the cortical substance, can be separated by the application of caustic 

 soda, when they appear as represented in Fig. 119. 



The dark spots, dots, or streaks, of the cortex are chiefly granu- 

 lar pigment ; cavities filled with air or fluid , or nuclei. 



430. Caustic Potash and Soda, soften and swell up the cortical 



