68 NATURE AND LIFE. 
elements of the earth’s crust. Thus they distinguish in 
the igneous systems granite, syenite, gneiss, diorite, etc. 
They then reduce each one of these rocks to a certain num- 
ber of immediate principles. Granite, for instance, will 
yield felspar, quartz, and mica. In like manner there are 
many degrees of complexity in the edifice of living beings, 
which are reduced by a series of analyses of a similar kind 
to a certain number of elements which are no less immedi- 
ate principles, that is, fundamental chemical substances. 
Robin was one of the first to understand the need of or- 
ganizing, systematically, our knowledge of these ingredi- 
ents, these materials for all vital elaboration and all or- 
ganic construction. 
Ancient chemistry admitted, without question, that the 
humors and tissues of the system are made of water, oil, 
earth, and salt. They sometimes added sulphur, phlegm, 
and alkali, All this was quite vague and uninstructive. It 
has since been admitted that the number of immediate prin- 
ciples is considerably more extended, and that their com- 
position is very intricate. The analyses of modern chem- 
istry have settled the exact nature and the chief proper- 
ties of these bodies, but have not yet reduced our knowledge 
of them to system. They have taught us that there exist 
in the system coloring matters, albuminoid ones, acids, 
salts, alkalies, alcohols, sugars, fats, and ethers. M. Robin, 
taking up certain hints of M. Chevreul, put the immediate 
principles in their true place, and classified them, while 
fixing their duty in the different parts of the system. 
These principles mark the passage from chemistry to 
biology. Regarded singly, in their molecular composition, 
their chemical function, and the transmutations they may 
undergo when influenced by reagents, they belong to 
chemistry. Looked at from the point of view of their 
number and their distribution in the living system, of the 
share they have in the growth of the animal’s organs and 

