OF THE SKIN. 153 



k 



terin, a non-saponifiable and uncrystallizable fat and bilin (Gallenstoff). 



The smegma of the horse possessed nearly the same constituents ; and 



among the salts, oxalate of lime; while in man, ammonio-phosphate of 



magnesia occurred. The watery extract contained neither albumen nor 



casein. 



An extensive desquamation of the entire horny layer of the epidermis, 

 such as takes place in the embryo and in many animals, does not occur 

 in man except in certain morbid states. On the other hand, its power 

 of regeneration is exhibited in other modes than those which have been 

 mentioned. Excised portions of the epidermis, for instance, are very 

 readily replaced, and with tolerable rapidity, so long as the corium be 

 not injured ; and, in fact, not by the immediate deposition of epidermis 

 in the wound, but only by the growing up of the whole epidermis from 

 below. If the eorium be injured as well, an epidermis is, indeed, formed 

 upon the substance of the cicatrix, but without any of the previous ele- 

 vations and depressions of the internal and external surface, because 

 the new corium has neither papillae nor ridges. If the epidermis be 

 raised up into a vesicle by acrid substances, e. </., Tartar emetic, a slight 

 burn, &c., the wall of the vesicle, which consists of the horny layer and 

 some few layers of cells of the mucous layer, never again becomes adhe- 

 rent ; but from the main substance of the mucous layer, which mostly 

 remains lying upon the papillre, a new horny layer is by degrees deve- 

 loped. 



If we inquire more minutely into the mode of regeneration of the epi- 

 dermis, there can, in the first place, be no doubt that it takes place in 

 the Malpighian layer, inasmuch as losses of substance of the horny layer, 

 e. g. a piece cut out, are restored not by the formation of a new portion 

 in the gap, but by the growth outwards of a horny layer fi-om below 

 (the wound remaining wholly unchanged), which gradually raises the 

 bottom of the wound, and brings it to a level with the surrounding epi- 

 dermis, the latter, in consequence of the pressure that it suifers from the 

 growing portion, becoming everted and exfoliating. The reason of this 

 phenomenon is to be sought, simply in this, that the non-vascular epider- 

 mis draws the materials which it requires for its nutrition and regenera- 

 tion from the superficial vessels of the corium. It is more difficult to 

 ascertain from what portion of the Malpighian layer the regeneration 

 proceeds. If a layer of cytoblastema and of free nuclei existed upon 

 the surface of the corium, as many authors suppose, we might acquiesce 

 in the view, that the epidermis grows by free cell-development in those 

 innermost layers which rest immediately upon it ; but such a cytoblas- 

 tema, as we have seen, does not exist, the stratum MalpigJiii being in- 

 variably formed by perfect cells ; and thence nothing remains, but to 

 suppose an endogenous cell-development around portions of contents in 



