HAIRS, FEATHERS, AND SCALES 17 



ward the ever-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 re- 

 semblance 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 thin but dense kind of bark, form- 

 ing the successive overlapping scales just described; (2) a 

 fibrous substance, 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, 1 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 elonga- 

 tion and narrowing of their constituent cells as they are 

 drawn 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. " a (3) Eunning through the very 

 centre of the fibrous portion may be sometimes discerned 

 a dark slender line, which is a sort of pith (medulla), com- 

 posed of minute roundish cells, filled with air, and arranged 

 in two or three rows. 



Th<3 bristles of the Hog bear much resemblance to the 

 human hair. On this slide is one, which you perceive is 



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

 was the result of several careful admeasurements of different hairs, taken from 

 childhood and adult age. 



2 Grant, "Outl. Comp. Anat." 647. 



