STRUCTURE OF HUMAN HAIR. FEATHERS. 707 



pletely isolated from its fellows, is found to be a long spindle 

 shaped cell. In the axis of this fibrous cylinder there is very 

 commonly 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 diffused through its 

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

 minute air-spaces, which cause it to appear 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 may be readily determined 

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

 (§§ 128, 129) ; 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 mounting 

 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 Canada balsam, 

 as may be thought preferable, the former menstruum being well 

 adapted to display the characters of the finer and more transparent 

 hairs, while the latter allows the light to penetrate more readily 

 through the coarser and more opaque. Transverse sections of Hairs 

 are best made by gluing or gumming several together, and then 

 putting them into the Section-instrument ; those of Human Hair 

 may be easily obtained, however, by shaving a second time, very 

 closely, a part of the surface over which the razor has already 

 passed more lightly, and by picking-out from the lather, and care- 

 fully washing, the sections thus taken-off. 



553. The stems of Feathers exhibit the same kind of structure 

 as Hairs ; their Cortical portion being the horny sheath that en- 

 velopes the shaft, and their Medullary portion being the pith-like 

 substance which that sheath includes. In small Feathers, this 

 may usually be made very plain by mounting them in Canada 

 balsam ; in large Feathers, however, the texture is sometimes so 

 altered by the drying-up of the pith (the cells of which are always 

 found to be occupied by air alone), that the cellular structure can- 

 not be demonstrated save by boiling thin slices in a dilute solution 

 of potass, and not always even then. In small Feathers, especially 



* Several writers regard this band of polygonal cells as 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 that the 

 transparent horny sheath, with its lines of imbrication, is the repre- 

 sentative 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. 



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