NITROGENOUS ORGANIC COMPOUNDS. 55 



normal nitrogenous food of plants, and that the ammonia of cul- 

 tivated soil is habitually converted into nitrous acid before its 

 absorption by their rootlets. 



(56.) Be this as it may, in all animal and vegetable nitro- 

 genised products of which the constitution is understood we 

 know, and in all other such principles have good reason to 

 believe, that the constituent nitrogen exists as a group apart as 

 a residue of, or proxy for, ammonia ready on the occurrence of 

 suitable conditions to regenerate that ammonia. As was observed 

 by Laurent some ten years ago, * nitrogen does not enter into the 

 constitution of organic substances on the same footing, so to 

 speak, as do the other bodies. Organic compounds seem to con- 

 sist of carbon, hydrogen, and oxygen only ; whilst nitrogen exists 

 therein but as the representative of ammonia on the one hand, or 

 of nitric acid on the other.' In organic compounds of natural 

 origin, nitrogen occurs only as a residue of ammonia ; whilst in 

 organic compounds of artificial origin, it occurs sometimes as a 

 residue of ammonia, as in cyanogen C 2 N 2 , sometimes as a residue 

 of nitric acid, as in azobenzide C 12 H 10 N 2 . 



(57.) In the artificial formation of organic compounds, then, there 

 are two distinct points for our consideration, namely, the building 

 up of the primary oxihydrocarbon molecules, and the combination 

 of the residues of these molecules with one another, and with am- 

 monia, to form complex organic principles. Now, the power of 

 combining the residues of aplone molecules with one another, so 

 as to form more or less complex bodies, has been in the possession 

 of chemists from almost the earliest days of organic chemistry, 

 and has been fully recognised to be in their possession. But, 

 somewhat strangely, it is only of late years that this well-known 

 power has been applied to the construction of some of themost 

 familiar components of animal and vegetable bodies. It is only 

 of late years, for instance, that chemists have produced stearin, 

 by putting together the residues of glycerin and the fatty acid ; 

 or sarcosine, by putting together the residues of acetic acid and 

 methylamine ; or hippuric acid, by putting together the residues 

 of benzoic acid and glycocine ; or taurine, by putting together 



