266 THE MICROSCOPE AND ITS REVELATIONS. 



the hair, especially after it has been macerated for some Vime in sulphuric 

 acid; and each of them, when completely isolated frora its fellows, is found 

 to be a long spindle-shaped cell. In the axis of tins fibrous cylinder there 

 is very commonly a band which is formed oi spheroidal cells; but this 

 i medullary' substance is usually deficient in the fine hair scattered over 

 the general surface 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 medullary axis in particular, are very commonly found to con- 

 tain air, giving it the black appearance shown at c. The difference be- 

 tween the blackness of pigment and that of air-spaces may be readily de- 

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

 ( 153, 154); and by watching the effects of the penetration of Oil of 

 Turpentine or other liquids, which do not alter the appearance of pig- 

 ment-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 pen- 

 etrate 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 Microtome; 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 carefully washing the sections thus 

 taken-off. 



663. The stems of feathers exhibit the same kind of structure as 

 Hairs; their cortical portion being the horny sheath that envelops 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 cannot be demonstrated save by boiling thin slices in a dilute 

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

 such as have a downy character, the cellular structure is very distinctly 

 seen in the lateral barbs, which are sometimes found to be composed of 

 single files of pear-shaped cells, laid end-to-end; but in larger feathers it 

 is usually necessary to increase the transparence of the barbs, especially 

 when these are thick and but little pervious to light, either by soaking 

 them in turpentine, mounting them in Canada balsam, or boiling them 

 in a weak solution of potass. In feathers which are destined to strike 

 the air with great force in the act of flight, we find each barb fringed on 

 either side with slender flattened filaments or 'barbules;' the barbules of 

 one side of each barb are furnished with curved hooks, whilst those of 

 the other side have thick turned-up edges; and as the two sets of barbules 

 that spring from two adjacent barbs cross one another at an angle, and 

 as each hooked barbule of one locks into the thickened edge of several 

 barbules of the other, the barbs are connected very firmly, in a mode very 

 similar to that in which the anterior and posterior wings of certain Hy- 



