EPIDERMIC CELLS. 



137 



Fig. 31. 



mation, 4 A : n ; or, in Chlorosis, A : J B. In Fever, the characteristic alteration in the con- 

 dition of the blood, appears to be an increase in the amount of Red corpuscles, with a. dimi- 

 nution in the quantity of Fibrine ; yet if a local inflammation should establish itself during 

 the course of a lover, the proportion of fibrine \vill rise; and this without any change in the 

 amount of corpuscles. Lastly, the effect of Loss of Blood has been shown by Andral's in- 

 vestigations, to be a marked diminution in the number of Red corpuscles, with no decided 

 reduction in the quantity of Fibrine, even when this is much above its normal standard ; and 

 in this condition of the blood, it has been observed by Remak that the Colourless corpuscles 

 are very numerous. 



6. Of Cells developed upon Free Surfaces. 



160. Next in independence to the cells or corpuscles floating in the animal 

 fluids, are those which cover the free membranous surfaces of the body, and 

 which form the Epidermis and Epithelium. Between these two structures 

 there is no essential difference, either in regard to their origin, their mode of 

 development, their situation, or their individual history ; but there is an im- 

 portant difference in the purposes which they respectively serve in the eco- 

 nomy. They both consist of cells, which are developed from germs furnished 

 by the subjacent membrane, which are nourished by its vessels, and which 

 are after a time cast off from its free surface to be replaced by a succeeding 

 generation ; but the contents of the cells vary in different situations, and give 

 peculiar characters to the tissue. The differences, however, are not more 

 striking between the Epidermis, or cellular covering of the external surface, 

 and the Epithelium, or cellular lining of the internal cavities, than those which 

 exist between the different portions of the Epithelium itself. For although 

 the Epidermis is distinguished by its comparatively 



hard, dry, horny character, whilst the Epithelium 

 is soft, moist, and deficient in tenacity ; yet we shall 

 hereafter find that, as all the Secretions of the body 

 are elaborated by the agency of the cells of the 

 latter, there must be as many varieties of endow- 

 ment, in these important bodies, as there are differ- 

 ences in the results of their action. 



161. The Epidermis, which usually forms a 

 thin semi-transparent pellicle, in close apposition 

 with the surface of the true Skin, but occasionally 

 presents a great increase in thickness, consists of 

 a series of flattened scale-like cells; which, when 

 first formed, are spherical ; but which gradually dry 

 up, their nucleus usually remaining visible. These 

 form several layers ; of which the deeper can be 

 seen very distinctly to possess the cellular character, 

 whilst the external layers are scaly ; and between 

 these, all stages of transformation may be traced. 

 The outer layers are continually being thrown off 

 by desquamation ; and new ones are as constantly 

 being formed below. They would seem to origi- 

 nate in germs supplied by the basement-membrane, 

 on whose surface they make their first appearance; 

 and their continued development takes place at the 

 expense of nutriment, which they draw through 

 that membrane, from the subjacent vessels. The 

 Epidermis is not itself traversed by vessels or 

 nerves; but it is pierced by the excretory ducts of 

 the sebaceous and sweat glands, and also by the 

 shafts of the hairs ; being, however, at the same 



12* 



Vertical section of Epidermis, 

 from palm of the hand ; a, outer 

 portion, composed of flattened 

 scales ; 6, inner portion, consist- 

 ing of nucleated cells; c, tortu- 

 ous perspiratory tube, cut across 

 by the section higher up. Mag- 

 nified 155 diameters. 



