596 



VEKTEBKATBD ANIMALS. 



are marked out by the delicate striae that maybe traced in lo^g^" 

 tudinal sections of the hair (b), may be separated from each other 

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

 some time in sulphm-ic acid; and each of them, when completely 

 separated from its fellows, is found to be a long spmdie-shapea 



Siruclure o( Haman IJair : — A, external siirfiice of llie shaft, showinfj the transverse slrise and 

 jng;yed liouiidary caused liy the imbrications of llie cortical substance ; B, longitudinal section of the 

 shufi, sliowinnr the fibrous character of the medullary suitstance, 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." 

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

 granules, either collected into patches, or difiused 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 difterence 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 cbies. 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 



' Several writers regard this band of polygonal cells as the "medullary'' snbstance, 

 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. 



