Chemical Obfervations on the Epidermis. 409 



and then mix the liquid with the colours, in order to ren- 

 der "them more oily and fluid. Care muft be taken that thi* 

 preparation be a little thick. 



XIV. Chemical Obl'cr-vations on the Epidermis. By J. A, 

 GHAPTAL. From Annales de Chimie, Vol. XXFL 



1 HE epidermis .of the human (kin is perhaps the bed 

 expanded and the eafieft to be detached of any, and for that 

 reafon I made it the fubject of the following experiments. 



The human fkin becomes fhrivelled in hot water, and 

 divides itfelf into two diftinct parts, the epidermis and the 

 cutis. The latter refembles then in its confiitence a foftened 

 cartilage. The continued action of warm water at length 

 diffolves the cutis, but does not fenfibly affect the epidermis. 

 Alcohol kept a long time in digeftion on the epidermis 

 likewife produces no effect. Cauffic alkali diffolves it, and 

 the fame effect is produced by lime, though more flowly. 

 There is then an analogy between the external covering of 

 the human body and that which covers filk. From thefe 

 obfervations we are authorifed to deduce the following con- 

 fequences, which may be applied, without overftraming the 

 principle, to the operations of tanning. 1. If we plunge 

 into a tanning infufion a piece of fkin covered by its epi- 

 dermis, the tan penetrates only on the flefh-fide : the other 

 fide is fecured from it by the epidermis, which is not fuiccp- 

 tible of any combination with the tanning principle, 



3. When the epidermis is removed by the operation of 

 liming, the tan then penetrates on both fides of the fkin. 



3. Lime, which is generally emplo\ ed for taking oft the 

 hair, feems to act only by diffolving the epidermis. Lime- 

 water has more action than undiffolved lime ; but its effect 

 ceafes the moment that the fmall quantity of lime held in 

 folution is combined with the epidermis : hence the ncccf- 

 fity of renewing the lime-water till the whole effect required 

 Reproduced, }:Vi qj 



