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 



