732 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



the strongest glue, were dissolved in equal quantities of the dilute acid, the colour 

 of the solutions was more intense, and the change produced by amnaonia was more 

 visible, according to the order of solubility and of tenacity. It is well known how 

 readily gelatin is dissolved by the caustic fixed alkalies: when therefore the varieties 

 of jelly or glue were added to boiling lixivium of caustic potash, they were soon 

 dissolved; and when added to saturation, a brownish viscid substance was formed. 

 I did not observe that any ammonia was produced, neither was any coal deposited, 

 after long boiling the solution in which there was an excess of alkali. The viscid 

 matter thus obtained, did not possess the properties of animal soap; for it neither 

 formed a permanent lather, when mixed and shaken with water; nor, when satu- 

 rated with acids, did it afford any precipitate; contrary to what happens, when 

 animal soap is thus treated. But, when the gelatinous substance was not pure; if, 

 for example, any parts of membrane, which are not soluble in water, were present, 

 then, in proportion to the quantity of this substance, the alkaline solution exhibited 

 more or less of the saponaceous characters; but these I never observed when pure 

 gelatin was employed. 



Gelatin, according to its quantity and quality, has a powerful influence on some 

 of the physical and chemical properties of the bodies in which it is present; by 

 these properties, I mean flexibility, elasticity, and putrescibility. So much has 

 been said already, in various parts of this paper, tending to prove how much the 

 degrees of flexibility and elasticity, in various animal substances, depend on their 

 gelatinous part, that little need be added; and when it is considered that bodies, 

 such as muscular fibre, membrane, sponge, hair, and cuticle, being deprived of 

 gelatin, and dried in the air, become rigid and brittle, no doubt can be entertained 

 but that this arises from the loss of the gelatinous substance; and, as an additional 

 proof, when bodies, such as nail, feather, quill, and tortoise-shell, which contain 

 little or no gelatin, are long boiled, and then dried in the air, like the former, 

 they are found to have suffered scarcely any alteration in their respective degrees of 

 flexibility and elasticity. 



As to putrefaction, it is obvious to every one, that certain parts of animals are 

 much more susceptible of it than others; and that when the carcase of an animal 

 begins to putrefy, the most humid and flexible parts are always first affected. Thus, 

 the viscera, muscles, and cutis, soon suffer a change ; while hair, feather, scale, 

 horn, hoof, and nail, remain unchanged, ages after the former have been decom- 

 posed ; and this is evidently caused by the gelatin and moisture, which are com- 

 bined in the former, and not in the latter, at least in any notable quantity. I have 

 already mentioned the progressive and comparative effects of boiling water, 

 and of dilute nitric acid, on the skin of the ox; and I have showed, 

 that while the cutis was completely dissolved, the hair remained untouched. These 

 effects are to be observed, in the same exact order, when a similar piece of skin is 

 exposed to putrefaction; for this commences in, and chiefly affects, the cutis, while 

 the hair is separated, unchanged in its quality. I do not therefore hesitate to assert, 



