HAIRS, FEATHEES, AND SCALES. 5 



these edges would be sinuous ; exactly as we see in 

 these lines upon the haii-. The effect and the cause are 

 the same in the two cases. 



A hair is closely analogous to the stem of a plant ; 

 inasmuch as it grows from a root, by continual additions 

 of ceEs to the lower parts, which, as they lengthen, push 

 forward the erer-lengthening tip. Indeed, in some of 

 the hairs which we shall presently look at, there is the 

 most curious resemblance to the stem of a palm, with 

 the projections produced by the successive growth and 

 sloughing of leaf-bases around the central cylinder. 

 Internally, too, the resemblance is remarkable ; for, if 

 we split a human hair, and especially if we macerate it 

 in weak muriatic acid, we shall find it composed of (1) 

 a thia but dense kind of bark, forming the successive 

 overlapping scales just described ; (2) a fibrous sub- 

 stance, extending from the bulb to the point of the hair. 

 By soaking the hair in hot sulphuric acid, this fibrous 

 substance resolves itself into an immense number of 

 very long cells, pointed at each end, and squeezed by 

 mutual pressure into various angular forms; " A. 

 human hair, of one-tenth of a line in thickness,* has 

 about 250 fibrils in its mere diameter, and about 50,000 

 in its entire calibre : so that these ultimate fibrils are 

 finer than those of almost any other known tissue, from 

 the great elongation and narrowing of their constituent 

 cells as they are dravni out into the shaft of the hair 

 during growth ; and hence the expanded bulb of the 

 hair, where the cells are yet spherical and soft."t (3) 



* This is nearly thrice as great as the diameter I had given above, 

 wluch was the result of several careful admeasurements of different hairs, 

 taken from childhood and adult age. 



f Grant. Outl. Comp. Anat. U1. 



