92 EPIDERMIS. [SECT. 48. 



the sudoriparous canals and hair-follicles, or their penetration into 

 the sudoriparous canals and mixture with the sweat. The mucous 

 layer, at all events, is easily permeated by liquids, as pathological 

 anatomy sufficiently shows (exudations, which permeate the mu- 

 cous layer, and raise up the epidermis in the form of vesicles ; easy 

 absorption after the horny layer and uppermost strata of the 

 mucous layer are removed by vesication). 



The so-called keratine, which constitutes the membranes of the 

 horny plates, is insoluble in water, easily soluble in concentrated 

 alkalies and concentrated sulphuric acid ; acetic acid also dissolves 

 it, after it has first become gelatinous, whereby it is distinguished 

 from the protein substance of the hair. It contains less sulphur 

 than that of the hair and nails, which may be the cause that salts 

 of lead, quicksilver, and bismuth colour the hair, but not the 

 epidermis. Besides, there is, according to Mulder, a jelly-like 

 matter in the horny layer, which is obtained by boiling in water, 

 and is said to yield gelatine. 



§ 48. Growth and Regeneration. — The epidermis possesses no 

 continuous growth dependent on intrinsic causes, and founded 

 on the vital relations of its cells, or of the corium ; it is essen- 

 tially a stable structure, which does not vary in its elementary 

 parts, but, like a cartilage, directs all its vital energies to maintain 

 itself as a whole (constant thickness of the entire epidermis and re- 

 lation of the rete Malpighii to the horny layer), and, in its indi- 

 vidual parts, always the same. Since, however, the removal of the 

 most external layers, if not necessarily, still accidentally, occurs 

 more or less over the entire body, the epidermis is contiuually under- 

 going repair of its lost substance, or, in other words, growing; its 

 vegetative life is thus manifested in a more perceptible manner. 

 In either case, however, the fluids requisite for the epidermis are 

 derived from the corium and its vessels. We may assume that in 

 every place a certain fixed quantity of plasma, corresponding to 

 anatomical and physiological conditions of the vessels of the cutis 

 and the thickness of the epidermis, penetrates the latter; and, 

 except as regards the more watery portion, destined for the forma- 

 tion of the cutaneous transpiration, when the epidermis is not 

 growing, simply fills its cells and plates, preserves their vital power, 

 and, at most, causes at times more abundant collections of pigment 

 in the rete Malpighii. If, on the other hand, the external layers 

 are removed, a certain quantity of plasma becomes free and ap- 

 propriable, and their regeneration takes place, which, if it steadily 



