THE. MECHANISM OF ORGANIC SYNTHESIS 131 



Thus by the action of simple catalytic agencies on sugar and ammonia 

 we can obtain the iminazol nucleus, and by easy transitions pass through 

 this to the purine nucleus with its contained ring, the pyrimidine 

 nucleus, found in the bases cytosine, uracil, &c., which occur in the 

 nucleins. 



With regard to the formation of the aromatic constituents of the 

 protein molecule, i.e. those containing the benzene and indol rings, 

 we have at present very little indication even of the lines along which 

 it might be possible to prosecute our researches. It haa been suggested 

 that inosite may represent some stage in the formation of the benzene 

 ring from the open chain found in the carbohydrates. Inosite haa 

 the same formula as glucose, namely, C 6 H 12 O e , but is a saturated ring 

 compound : 



CHOH 



CHOH 



CHOH 



CHOH 



CHOH 



CHOH 



and may be expected to be formed as a result of polymerisation of 

 formaldehyde. We have no evidence, however, of the possibility of 

 such a formation, and the relations of this substance with the benzene 

 compounds are by no means intimate. It is of such universal occur- 

 rence, both in plants and animals, that it is difficult to refrain from the 

 suspicion that it may play some part as an intermediate stage between 

 the fatty and the aromatic series. 



Since plants are able to manufacture all these varied substances out 

 of the products of assimilation of carbon and ammonia or nitrates, 

 they must also find no difficulty in transforming one amino-acid into 

 another, and we know that most plants can procure their nitrogen 

 from a solution of a single amino-acid as well as from a nutrient fluid 

 containing the nitrogen in the form of ammonia. In animals the 

 power of transforming one amino acid into another, of one group 

 into another, is probably strictly limited. So far as we know, nearly 

 all the amino-acids utilised in the building up of the animal proteins 

 are derived directly from those contained in the food. On the other 

 hand, we have evidence in the animal body of synthesis of the purine 

 bodies, and therefore of the pyrimidine and iminazol rings. The hen's 

 egg at the beginning of incubation contains very little nuclein, 

 nearly the whole of its phosphorus being present in the form of phos- 

 phoproteins and lecithin. As incubation proceeds these substances 

 disappear, their place being taken by the nucleins which form the chief 

 constituent of the nuclei of the developing chick. In the same way the 

 ovaries and testes of the salmon are formed during their sojourn in 



