358 



THE MICROSCOPE. 



more minute, and exhibit no trace of strise on their surfaces ; but those 

 taken from dark-coloured hairs have colouring-matter deposited on 

 them in small patches. In some cases they appear to terminate in a 

 pointed process, like the quill part of butterflies' scales ; and in others 

 the free margin is serrated. By scraping, many of them will be 

 detached separately ; but in some few cases as many as four or five will 

 be found joined together : in the larger hairs the cellular structure of 

 the interior, as well as the fibrous character of the shaft, are better seen 

 after the scales have been removed. 



The hair owes the greater part of its colour to pigment-cells : as 

 these decay, and become gradually divested of their colouring-matter, 

 they appear whitened, or "turn grey." These hexagonal cells also give 

 colour to the skin of the negro, and are situated immediately beneath 

 the transparent coat. A small portion is shown in fig. 169, No. 4, 

 the vacant space denoting the situation of a lost hair. 



Certain parts of the skin and mucous membranes are especially sup- 

 plied with papillae, 

 which serve as or- 

 gans of touch ; ne- 

 vertheless, through- 

 out the skin there 

 are papillce more or 

 less sensitive ; but 

 it is only at the ex- 

 No. 1. A section of the skin of finger, showing the vascular tremities of the fin- 

 network oipapiUce at the surface of the cutis. No. 2. Ca- gers, lipS, and in a 

 pfflary network and distribution of papilte of the tongue, f^^ ^^^^^ situations, 



that these are highly developed, as in fig. 170. Papillae are either fili- 

 form or tubeform, and have entering into them nerves and blood- 

 vessels ; the former supplying the sensibility of the skin, and termi- 

 nating in loops, as shown in fig 171. 



In Plate XIV., No. 1, we have represented a vertical section of the 

 skin, drawn under a :|^-inch object-glass. 



The skin is the seat of two processes in particular ; one of which is 

 destined to free the blood from a large quantity of fluid, and the other 

 to draw off" a considerable amount of solid matter. To effect these pro- 

 cesses, we meet with two distinct classes of glandulse in its substance : 

 the sudoriferous, or sweat glands; and the sebaceous, or oil-glands. 

 They are both formed, however, upon the same simple plan, and can 

 frequently be distinguished only by the nature of their secieted product. 



The sudoriferous or perspiratory glands form small oval or globular 



fig. 170. 



