OF THR HAIHs. 



1 I I 





lanugo and coloured hairs of the head, but is usually present in 

 the thick, short hairs, Fjr , 6g 



and in the stronger 

 long ones, as well as 

 in the white hairs of 

 the head. If white 

 hairs be boiled with 

 caustic soda until 

 they swell and coil 

 up, we can often, by 

 the use of simple 

 pressure,demonstratc 

 without further trou- 

 blc,the cellular struc- 

 ture of the medullary 

 cylinder, which is 

 then transparent for 

 transmitted light (fig. 

 65 a). If a hair thus 

 treated be carefully 



teased out, it is easy to isolate the medullary cells, 

 cither in aggregate masses, or even completely 

 separate (fig. 69). They are rectangular or quadran- 

 gular, rarely rounded or fusiform of 0-007 — 001'" 

 in diameter, occasionally containing dark, fat-like 

 granules, and often when the alkali has not acted too strongly, 

 a rounded clear spot of 0-0016 — 0-002'", which is plainly the 

 rudiment of a nucleus, and which also seems to swell up 

 somewhat in soda. 



In fresh hairs, the medulla in the shaft is silvery white or 

 dark, an appearance which, as many more favorable objects 

 show, arises from rounded-angular, granular corpuscles, black 

 (opaque) or of a brilliant white, according to the illumination, 



a»K 





'■■%' 



< 1 i / 



Fig. 69. 



Fig. 68. A portion of the root of a dark hair slightly acted upon by caustic soda, 

 x 250: a, medulla, still containing air, and with cells, which appear pretty distinct; 

 b, cortex with pigment spots ; e, inner layer of the epidermis ; d, outer layer of it-; 

 e, inner layer of the inner root-sheath ( Huxley's layer) ; /, outer fenestrated layer 

 (Henle's layer). 



Fig. 69. Eight medullary cells, with pale nuclei and fatty granules, from a hair 

 treated with soda, x 350. 



i. 12 



