14 BIOLOGY. [Book i. 



products. We can succeed in substituting magnesia for lime in 

 the shells of eggs. We can, in fats, replace hydrogen by chlorine, 

 without modifying essentially the properties of the compound. 

 Chemical S3Tithesis has also tried to reproduce the simplest of 

 the azotic organic substances. There has been a direct repro- 

 duction of urea, of taurine, of glycocoll in the laboratory ; and 

 if the. true albuminoidal bodies have hitherto defied the efforts' 

 of synthetic chemistry, we may almost with certainty predict 

 that they will not defy them always. It will then be possible 

 to appropriate direct from the mineral world fibrin^, albxunirW 

 casein^ and so on, that is to say, the special, the most needful 

 alimeiits of man. This grand discovery must inaugurate for 

 civilised communities a new era. It must be for man a real 

 enfranchisement, by diminishing in a prodigious measure' the sum 

 of muscular labour, to which for more or less duration and 

 progression he is now doomed. 



These preliminaries settled, we are able to enumerate the 

 various groups of simple or compound substances, which by their 

 union constitute the bodies of organised beings. M. Oh. Robin 

 has given an excellent classification of the,se substances or imme- 

 diate principles} According to him, the immediate principles are 

 the ultimate solid bodies, liquid or gaseous, to which we can 

 reduce the liquid or solid organised substance, the humours and 

 the elements. But in order that these ultimate materials may 

 merit the name of immediate principles, M. Eobin thinks they 

 mdst be obtained without chemical decomposition, by simple 

 coagulations and successive crystallisations. 



These bodies, which, by their innermost blending, their reci- 

 procal dissolution, constitute the semi-solid organised substance, 

 can be grouped into three classes : 



1. The first class comprehends the crystalHsable or volatile 

 bodies without decomposition, having a mineral origin and comina 

 forth from the organism as they had entered it (water, certain 

 salts, and so on). 



2. The immediate principles of the second class are also 



1 Charles Eobin, Lefom sv/r les Sxvrmwrs, Paris, 1867. 



