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- 
Juble m hot water; albumen is soluble in cold, and inso- 
luble in hot water; and fibrin is equally msoluble 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, im 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 followmg 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 Brrzxetrus 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+ 1s 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 Harcuert,’ 
“‘ Chemical Experiments on Zoophytes; with some Observations on the 
eomponent Parts of Membranes.” Phil. Trans. 1800, p. 327. 
+ Annals of Phil. ii. p. SSO. 
VOU. I. i 
