118 PHYSIOLOGY 



exposed to light, methyl iminazol is formed in large quantities. Windaus 

 and Knoop imagined that in this process glyceric aldehyde and formaldehyde 

 are first formed, and that these then interact with ammonia to form methyl 

 iminazol. 



CH 3 



C NH 



II 

 CH N 



It is interesting to note that if we attach to this compound carbamide 

 or urea we obtain a body belonging to the class of purines. Xanthine, 

 for instance, would have a formula 



NH CO 



I I 

 CO C NH 



I II > H 



NH CH W 



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 has been suggested that inosite may 

 represent some stage in the formation of the benzene ring from the open chain 

 found in the carbohydrates. Inosite has the same formula as glucose, 

 namely, C 6 H 12 6 , but is a saturated ring compound : 



CHOH 



CHOH 



,CHOH 

 JCHOH 



CHOH 



CHOH 



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

 hyde. 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 occurrence, 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 



