264: 



THE MICROSCOPE AND ITS REVELATIONS. 



same manner namely, by an increased production of epidermic cells at 

 the bottom of a flask-shaped follicle, which is formed in the substance of 

 the true skin, and which is supplied with abundance of blood by a spe- 

 cial distribution of vessels to its walls. When a hair is pulled-out 'by its 

 root/ its base exhibits a bulbous enlargement, of which the exterior is 

 tolerably firm, whilst its interior is occupied by a softer substance, which 

 is known as the 'pulp;' and it is to the continual augmentation of this 

 pulp in the deeper part of the follicle, and to its conversion into the pe- 

 culiar substance of the hair when it has been pushed upwards to its nar- 

 row neck, that the growth of the hair is due. The same is true of feath- 

 ers, the stems of which are but hairs on a larger scale; for the 'quill ' is 

 the part contained within the follicle answering to the ' bulb ' of the hair; 

 and whilst the outer part of this is converted into the peculiarly-solid 

 horny substance forming the ' barrel' of the quill, its anterior is occupied, 

 during the whole period of the growth of the feather, with the soft pulp, 



FIG. 449. 



FIG. 450. 



FIG. 451. 



Fig. 449. Hair of Sa- 

 ble, showing large 

 rounded cells in its 

 interior, covered by 

 imbricated scales or 

 flattened cells. 



450. Hair of 

 Musk-deer, consisting 

 almost entirely of po- 

 lygonal cells. 



A, Small Hair of Squirrel : B, Large Hair 

 of Squirrel: c, Hair of Indian Bat. 



only the shrivelled remains of which, however, are found within it after 

 the quill has ceased to grow. 



661. Although the hairs of different Mammals differ greatly in the 

 appearances they present, we may generally distinguish in them two ele- 

 mentary parts namely, a cortical or investing substance, of a dense horny 

 texture, and a medullary or pith-like substance, usually of a much softer 

 texture, occupying the interior. The former can sometimes be distinctly 

 made- out to consist of flattened scales arranged in an imbricated manner, 

 as in some of the hairs of the SaUe (Fig. 449) ; whilst, in the same hairs, 

 the medullary substance is composed of large spheroidal cells. In the 

 Musk-deer, on the other hand, the cortical substance is nearly undistin- 

 guishable; and almost the entire hair seems made up of thin- walled poly- 

 gonal cells (Fig. 450). The hair of the Reindeer, though much larger, 

 has a very similar structure; and its cells, except near the root, are occu- 

 pied with hair alone, so as to seem black by transmitted light, except 

 when penetrated by the fluid in which they are mounted. In the hair of 

 the Mouse, Squirrel, and other small Eodents (Fig. 451, A, B), the corti- 



