COMPOUNDS OF ORGANIZATION. 65 



The four substances which we have now enumerated, 

 constitute the soft parts of animals, and enter into the com- 

 position of the hard parts and of the fluids. They are 

 readily distinguishable from one another. Extractive alone 

 is soluble in alcohol ; gelatine is insoluble in cold, but so- 

 luble in hot water ; albumen is soluble in cold, and inso- 

 luble in hot water ; and fibrin is equally insoluble in hot 

 and cold water. They are variously mixed or united ; 

 and as they consist of the same elementary principles, 

 chiefly carbon, hydrogen, oxygen and azote, it is probable 

 that they are changed, the one into the other, in many 

 cases, by the living principle, a transmutation which the 

 chemist has succeeded in accomplishing, and which may 

 soon be of advantage in the arts. The proportion of car- 

 bon appears to be least in gelatine, and greatest in fi- 

 brin *. 



The following substances, which occur in the composi- 

 tion of animals, are not so exclusively distributed, although 

 equally entitled to our attentive consideration. 



5. Mucus. This term has been applied to various se- 

 creted fluids, whose properties differ considerably from .one 

 another. Hence the greatest uncertainty prevails respect- 

 ing the characters common to all kinds of mucus, and those 

 which distinguish particular varieties or species. The fol- 

 lowing characters are assigned by BERZELIDS to the mucus 

 of the saliva and of the nose, which we shall quote in his 

 own words, for the purpose of avoiding mistakes. 



" The mucus of the saliva^- is readily procured by 

 mixing saliva with distilled water, from which the mucus 



For farther illustrations respecting the nature of gelatine, albumen 

 and fibrin, the reader is referred to an admirable paper by HATCIIETT, 

 " Chemical Experiments on Zoophytes ; with some Observations on the 

 component Parts of Membranes." Phil. Trans. 1800, p. 327. 



f Annals of Phil. ii. p. 380. 



VOL. I. E 



