THE INTEGUMENTS AND CLOTHING OF MAMMALIA. 149 



sembles the slough of a snake, which is, in fact, the epidermis of that 

 reptile. In the Cetacea it is smooth, and lubricated with an oleaginous 

 secretion, so as to prevent the macerating action of the water. 



Such, then, are the nature and composition of the common integu- 

 ments, or skin, of the body : but the skin has appendages, destined for 

 various purposes warmth, defence, or ornament, which now claim 

 notice. These are hair, bristles, wool, and spines, scales and plates, 

 nails and horns. 



Hair and wool, though they differ from each other in certain structural 

 peculiarities, are intrinsically the same ; and, therefore, until the differ- 

 ences be defined, they may be considered as one. Hair (including bristles 

 and wool) is of a horny texture, and grows from a secreting vascular 

 bulb, or root, seated below the cutis : from this bulb the hair is gradually 

 evolved : passing through a canal of reflected integument, which traverses 

 the corium, it emerges from the surface of the skin, and continues to 

 grow till it has acquired its full development. The intimate structure of 

 hair has been the subject of very opposite opinions. Leuwenhoeck 

 says, that hair consists of little strings, of which a thousand or more, 

 according to the thickness of the hair, combine to make it up : but 

 he was not able to determine the nature of these strings, though he 

 is disposed to consider them hollow. (See Phil. Trans. 1678, xii.) 

 Hooke (Micographia), speaking of the hairs of the head, in the human 

 subject, states, that, for the most part, they appeared to be cylindrical, 

 according to his microscopic experiments ; that some of them were 

 prismatic ; but that, generally, they were nearly round : he also ob- 

 serves that, throughout their length, they were transparent, although not 

 very clear ; the end nearest the root resembling a black, transparent 

 piece of horn. The roots of the horn were apparently smooth, and 

 tapering inward, somewhat in the form of a parsnip ; but were, as far 

 as he ascertained, destitute of filaments, or any vessels like the fibres of 

 a plant. The top, when split (as long hairs frequently are), resembled 

 the end of a stick beaten until frittered, there being, sometimes, half 

 a score splinters, or more. According to the same writer's experiments, 

 these hairs appeared to be solid, cylindrical bodies ; not pervious, like a 

 cane or bulrush, nor having an internal pith, or external rind, as in 

 Horse's hair, Deer's hair, and the bristles of a Cat. 



It is singular, however, that the hair of the Horse and of the Deer, 

 and the whiskers of the Cat, should be pervious, and that the hair of 

 the head in Man should be solid : the inference, granting the correctness 

 of the statement respecting the hair of the Horse and Deer, is, that, 

 although Mr. Hooke failed in his endeavours to ascertain it, human hair 

 has the same internal structure ; and many circumstances tend to prove, 

 that it consists of an external rind, or sheath, and an internal pulp, or 



