gn^ Struflure and Ccmpofttkn of tht Skins of AminaU. 



immerfing the fkins. For this fubftance, when depofited, attaches itfelf to the furface of 

 the fkins, where it forms a coating more or lefs thick, which foils them, clofes their pores, 

 and retards in a fmall degree the dircft adion of the tan. 



2. The lixivium of tan, particularly when highly concentrated, and prepared in hot wea- 

 ther, acquires after a few days a vinous fmell, which feems to announce a commencement 

 of fermentation, and might lead to an apprehenfion that its progrefs might impair the tanning 

 properties. In order to afcertain how far thefe notions might be well founded, different 

 vegetable acids were mixed with the tanning lixivium, but none of them fenfibly altered its 

 properties. And ftill more we may add, that for near two years a bottle of the infufion of 

 tan has been kept in the laboratory, and, in fpite of the alterations of temperature to 

 which it has been expofed, and the change ncceffarily produced by the contaft of air, its 

 properties appear the fame, and it is dill daily ufed with advantage as a re-agent to afcer- 

 tain the prefence of gelatin. 



As a knowledge of the properties of tan affords obfcrvations of importance, which confti- 

 tute the bafis of Seguin's method, wc have not been apprehenfive of dwelling too long on 

 the fubiecl ; but we (hall confine our remarks on the ftrudure and chemical compofition 

 of the (kin to a few general confiderations. 



This membrane, as is (hewn by anatomifts, is effentially formed of a great number of 

 iaminx or fibres, which are white, broad, ftiort, and clofely adherent, but interwoven, ani 

 difpofed in different diredions, fo as to leave between them an infinity of fmall fpaces or 

 pores. From this con(lrud\ion it exhibits a denfe but foft fpongy texture, and is fufceptible 

 of extenfion and contraclion. In the midft of this fubftance are found a great number of 

 nerves and veffels of different kinds, the very fine and multiplied ramifications of which fervc 

 to fupport and maintain the lamellated ftru£lure of the fkin, and convey into the vacuities 

 between the fibres thofe fluids which ferve for the fupport and nutrition of this membrane. 

 The external part is tlie epidermis. This thin tranfparent membrane is of a very different 

 texture. It contains neither the apparatus of veffels, nor the difpofition of'fibres or laminse, 

 which by their interfeftion form a kind of fpongy net-work. It is in fome meafure a fimple 

 uniform covering, which prcfents no diftindl organization, but adheres ftrongly to the fliin, 

 entering into its folds and numerous porofities. Laftly, the hairs are implanted in the Ikin 

 by a fort of bulb or oval root, interfperfed with fmall veffels filled with a kind of mucus. 



The compofition of the ficin, the changes it undergoes by different preparations.by chemical 

 agents, and the properties it acquires in thefe feveral ftates, prefent other confidcrations. 



If ihe frefli fkin of an adult animal be macerated for fome hours in water at the tem- 

 perature of the atraofphere, and if, to accelerate the effe£l, agitation and preffure be ufed, % 

 reparation is made of the blood, the juices, and the different foluble fubftances contained 

 in the veffels or vacuities ; and by examining the nature of the matter thus extra£led, it is 

 found that a fmall portion only confifts of gelatin, which has little confiftence or tenacity. 

 Subfequent macerations, at the fame temperature, afford no more gelatin, the fibrous texture 

 remains infoluble, and undergoes no further lofs. It therefore appears, that in the natural 

 ftate the Ikin contains but a fmall portion of gelatin perfe£lly formed, and foluble. It 

 may even be apprehended, that the fmall quantity obtained by the firft maceration was. 

 merely included in the pores of the Ikin adherent to the furface of the fibres ; and 

 that the vital force had not yet time to adimilate and convert it to the ftate of fibre. 



-, But 



