596 



VERTEBRATED ANIMALS. 



are marked out by the delicate striae that maybe traced in longi- 

 tudinal sections of the hair (B), maybe separated from each other 

 by crushing the hair, especially after it has been macerated for 

 some time in sulphuric acid; and each of them, when completely 

 separated from its fellows, is found to be a long spindle-shaped 



Structure of Human Hair: A. external surface of the shaft, showing the transverse striae and 

 jagged boundary caused by the imbrications of the cortical substance ; B, longitudinal section of the 

 shaft, showing the fibrous character of the medullary substance, and the arrangement of the pig- 

 mentary matter; c, transverse section, showing the distinction between the transparent envelope, 

 the cylinder of medullary substance, and the cellular centre; D, another transverse section showing 

 deficiency of central cellular substance. 



cell. In the axis of this fibrous cylinder, there is very com- 

 monly a band which is formed of spheroidal cells ; but this is 

 usually deficient in the fine hairs scattered over the general sur- 

 face of the body, and is not always present in those of the head. 1 

 The hue of the hair is due, partly to the presence of pigmentary 

 granules, either collected into patches, or diffused through its 

 substance ; but partly also to the existence of a multitude of 

 minute air-spaces, which cause it to appear as dark by transmitted 

 and white by reflected light. The cells of the axis-band, in par- 

 ticular, are very commonly found to contain air, giving it the 

 black appearance shown at c. The difference between the black- 

 ness of pigment and that of air-spaces, maybe readily determined 

 by attending to the characters of the latter as already laid down 

 ( 98, 99) ; and by watching the effects of the penetration of 

 oil of turpentine or other liquids, which do not alter the appear- 

 ance of pigment spots, but obliterate all the markings produced 

 by air-spaces, these returning again as the hair dries. In mount- 

 ing hairs as microscopic preparations, they should in the first 

 instance be cleansed of all their fatty matter by maceration in 

 ether ; and they may then be put up, either in weak spirit or in 



1 Several writers regard this band of polygonal cells a's the "medullary" substance, 

 and the fibrous structure which forms the principal body of the hair, as the "cortical" 

 substance; the transparent sheath receiving some separate designation. To the Author, 

 however, it appears perfectly clear that the transparent horny sheath, with its lines of 

 imbrication, is the representative of the cortical substance of other hairs ; and that its 

 entire contents, whether polygonal cells or cells elongated into fusiform fibres, must be 

 considered as equivalent to their medullary substance. 



