HAIR. 



[ 376 ] 



HAIR. 



of colour, and the presence of fungi. When 

 the colour entirely vanishes, and the hair 

 becomes white or grey, the cells of the me- 

 dulla contain abundance of air. This arises 

 from degeneration or impaired nutrition; 

 the liquid contents of the cells are not sup- 

 plied in sufficient quantity ; they therefore 

 evaporate, and the cells being prevented 

 from collapsing by their adhesion to each 

 other and to the firm cortex, become filled 

 with air, which replaces what would other- 

 wise constitute a vacuum. Fungi are found 

 in FAVUS upon the cortex of the hair, 

 within the follicles, and even within the 

 hair itself, as is stated. In Porrigo decal- 

 vans also, fungi are stated to occur in the 

 hairs. 



The principal differences between the hair 

 of man and of animals, and that of animals 

 from each other, relate to 1, the size; 2, 

 the relative proportions of the cortical and 

 medullary structures ; 3, the locality of the 

 pigment ; 4, the arrangement of the medul- 

 lary cells ; 5, the comparative amount of 

 true hair, and woolly hair, down, or wool ; 

 and 6, the size and projection of the super- 

 ficial cortical cells or scales. 



Of these we shall give a brief sketch 

 (PI. 1. figs. 1-3, and PL 29). 



The hair of the Mammalia generally is 

 formed upon the same plan as that of man ; 

 great variety, however, exists in its com- 

 plexity of structure and the arrangement of 

 the component parts. 



Quadrumana (PI. 29. figs. 4 & 5). In the 

 monkey (Indian) (fig. 4), the hair presents 

 much of the same structure as in man; the 

 pigment is confined to the cortex, but the 

 air-cells of the medulla are larger and less 

 crowded ; this is seen to a greater extent in 

 the hair of the lemur (fig. 5). 



Cheiroptera. In the bats (PL 1. fig. 2; 

 PL 29. figs. 6 & 7), a striking character is 

 the peculiar development of the cortical 

 scales of the surface. In the hair of the 

 common bat (PL 1. fig. 2), which is one 

 of the TEST-OBJECTS, and Australian bat 

 (PL 29. fig. 7), this character is not so 

 striking as in that of the Indian bat (fig. 6), 

 in which the scales are grouped in whorls 

 at pretty regular intervals along the shaft, 

 and project considerably beyond the sur- 

 face. The pigment is principally confined 

 to these whorled scales. In some of the 

 white hairs of the bat, the individual scales 

 are very beautifully seen (PL 1. fig. 2 c). 



Insectivora. The hair of the mole (PL 

 29, fig. 8) bears some resemblance to that 



of the bats : but the cells of the medulla 

 are very distinct. (See SPINES.) 



Camivora (figs. 9-13). In this Order the 

 structure of the hair varies considerably. 

 In the lion (fig. 9) the cortical cells are di- 

 stinct, but not projecting; the medullary 

 cells are very numerous, and the air-spaces 

 minute, but closely aggregated, as we often 

 find them in the human hair. In the bear 

 (fig. 10), the large hairs present much the 

 same structure as in the lion ; the wool- 

 hairs differ strikingly from these, however, 

 in the distinctness of the cortical and me- 

 dullary cells. 



Pachydermata (figs. 14-17). In this Order 

 the hairs present a development correspond- 

 ing with that of the skin; being very thick 

 and complex in structure. In the elephant 

 (fig. 15, transverse section), each hair re- 

 sembles a number of hairs fused together. 

 Scattered through its substance are pale 

 spots formed by cells containing little or no 

 pigment, with an irregular perforation in 

 each, probably arising from rupture of the 

 cells. Surrounding these medullary centres 

 are innumerable cortical cells loaded with 

 pigment. In the pig (fig. 16), the distinc- 

 tion between the cortex and medulla is not 

 well marked, and the cells assume a radial 

 direction, as indicated by those which con- 

 tain most pigment. In the Cheiropotamus 

 (fig. 17) the distinction is more evident. 



Rwminantia (figs. 18-22). In this Order 

 the hair presents great variety. In the 

 camel (fig. 18) and dromedary (fig. 19), the 

 true hair exhibits much the same structure 

 as that of the higher Orders, whilst in the 

 deer (fig. 20, moose-deer; fig. 21, musk-deer) 

 the medullary portion is enormously deve- 

 loped at the expense of the cortical portion; 

 in no hair is the cellular structure more 

 distinct than in the two latter, the medulla 

 closely resembling a piece of vegetable cel- 

 lular tissue. The wool-hair in this class 

 presents the characteristic structure. That 

 of the camel (fig. 18 b) agrees in structure 

 with the type of wool from the sheep 

 (fig. 22) in its softness, flexibility and 

 waviness, and in the distinctness of the 

 cortical cells. 



Edentata (figs. 23 & 24). The difference 

 between the hair of the three-toed sloth 

 (fig. 23) and that of the armadillo (fig. 24) 

 is well-marked. In the former, the cor- 

 tical cells take a remarkably oblique or 

 radiating course, whilst in the latter they 

 run longitudinally. 



Eodentia (figs.' 25-35). In this Order the 



