and Observations on the component Parts of Membrane. 367 



had opportunities of frequently observing the various degrees 

 of viscidity and tenacity which characterize mucilage, size,* 

 and glue. 



The difference in the viscidity and tenacity of the varieties 

 of these substances, is evidently an inherent quality, and not 

 caused by the degree of mere inspissation : if this was the case, 

 mucilage, size, and glue, when dry, would be of an equal quality, 

 which is, however, contrary to daily experience ; for the varieties 

 of glue are not of equal tenacity. And it is well known, that 

 glue made from certain parts of animals, such as the skin, is 

 more tenacious, and of a better quality, than that which is 

 made in some places from feet and sinews. 



Moreover, when even the same part is employed, which has 

 been taken from two animals of the same species, an evident 

 difference is found, according to the comparative age of the 

 animals; for the best and strongest glue is always obtained 

 from the more aged animals, in whom the fibre is found to be 

 the most coarse and strong. But a longer continued boiling 

 appears requisite in order to extract it ; and the more viscid glues 

 are obtained, from the substances which afford them, with greater 

 difficulty than those of a less viscid quality, which may more 

 properly be called size : this difference is to be observed, when 

 muscle is boiled with repeated and frequent changes of water. 



Gelatin thus obtained, whether in the state of mucilage, size, 

 or glue, when completely dried, is affected by water accord- 

 ing to its degree of viscidity : for, when cold water is poured 



* The term size is employed, throughout this paper, to denote that modification of 

 gelatin which appears to be intermediate, between mucilage and the most viscid and 

 tenacious gelatinous substances or glues. The weaker kinds of glue may therefore 

 come under this denomination. 



MDCCC. 3 B 



