HAIR. 



[ 306 ] 



HAIR. 



pliuric or some other acid at a gentle heat, 

 it becomes at first resolved into plates or 

 fibres (fig. 297 B) of the most varied sizes, 

 both as to length and breadth ; but if the 

 action of the acid be continued, these fibres 

 become separated into cells (fig. 297 ^)- 

 These cells present uneven surfaces, and a 

 more or less elliptical outline, their true form 

 being spindle-shaped ; but they are mostly 

 flattened and angular, or cm-ved from mutual 

 pressure, resulting from their aggregation 

 into the shaft of the hah. The cells are 

 about 1-300 to 1-500" in length, and from 

 1-6000 to 1-2200" in breadth. They mostly 

 contain elongated, dark-looking nuclei, 

 1-400 to 1-1100" in length; these are well 

 seen in a colourless hair, heated with soda or 

 potash (fig. 298 Ab, and jB) ; in colom'ed 



Fig. 298. 



Magnified 350 diameters. 



A, Portion of a white hair after treatment with soda. 

 a, nucleated cells of medulla, free from air ; b, cortical 

 substance with fibrillation and linear nuclei ; c, cuticle. 

 B, three isolated nuclei from the cortex. 



hair they also contain pigment-granules, to 

 which the colour of the hair is principally 

 owing. The pigment-granules are exceed- 

 ingly minute, about 1-50,000" in diameter, 

 rounded, and as existing in the hair, are 

 mostly arranged in linear groups, their 

 colour and number varying with that of the 

 hair. The pigment-granules are best sepa- 

 rated by the action of caustic potash or soda, 

 and they frequently exhibit molecular motion. 



The striated and dotted appearance of the 

 shaft of hairs is not produced simply by the 

 nuclei, nor by the pigment, but arises in 

 part also from the unequal refraction of the 

 light by the various parts of the cells, and 

 from the presence of minute spaces filled 

 with air. The nature of each can always be 

 determined by attention to the principles 

 laid down in the Introduction. 



Towards the bulb, the cells of the cortex 

 are more distinct, less elongated, and as well 

 as the nuclei more easily isolated when 

 treated with acids (fig. 299) ; whilst in the 



Fig. 299. 



Fig. 300. 



m 



Magnified 350 diameters. 



Fig. 299. Two striated cells from the cortex of the root 



close aboTe the bulb, with nuclei. 

 Fig. 300. Cells from the deepest portions of the bulb : 



a, from a coloured bulb, with pigment- granules and 



partly concealed nuclei ; b, from a white hair, with 



distinct nuclei and a few granules. 



bulb itself they are round (fig. 300), 1-4000 

 to 1-1800" in diameter, closely crowded, and 

 sometimes containing only a colourless 

 nucleus, at others pigment-granules. 



The medulla, like the cortex, consists of a 

 number of cells. Its structure is best ob- 

 served in a hair which has been treated with 

 soda or potash. The cells are then seen to 

 be arranged in one or more linear series 

 (fig. 298 a) ; they are angular or rounded, 

 1-2000 to 1-1000" in diameter; and if the 

 action of the alkali has not been too long 

 continued, they exhibit a nucleus ; they fre- 

 quently also contain one or more granules 

 or globules of fat (fig. 302). In the shaft 

 and upper part of the root of the hair, these 

 cells contain air, which gives them a dark or 

 black appearance by transmitted light ; and 

 it w^as the generally received opinion, until 

 we pointed out the error several years ago, 

 that this darkness or blackness arose from 

 the presence of pigment. The contrary, 

 however, may be easily proved by macerating 

 the ban* in oil of turpentine or any liquid, 

 when the air escapes in bubbles and becomes 



