140 THK r6le of nitrogen in plant-metabolism, v., 



green plants, nitrates can contribute to the formation of 

 protein, without light, provided only that carbohydrates be 

 supplied ; and that this change always begins by a reduction 

 of the nitrates, through nitrites to ammonia. Now one of 

 the easiest methods of lengthening the carbon-chain (in vit?-o) 

 is through the formation of nitrils by hydrocyanic acid ; and 

 Treub* believes that, in the presence of glucose, nitrates are 

 directly transformed into nitrils as the first assimilation- 

 product. This sudden step is difficult to comprehend from 

 the chemical point of view ; it is, however, supported by *:he 

 recent experiments of Ravenna and Pelif, where the produc- 

 tion of hydrocyanic acid in Sorghum vulgare was traced to 

 the simultaneous action of nitrates and carbohydrates, 

 favoured by light. These authors state that hydrocyanic acid 

 appears to be the simplest substance which can be detected as 

 taking part in the synthesis of protein. 



Instead of the above sudden transformation of the nitrate, 

 it seems more probable that the enzymic reduction of nitrate 

 to ammonia is the natural one. It is then easy to follow the 

 subsequent stages along certain possible directions well known 

 in organic chemistry, and which can easily be demonstrated. 

 (1) The formation of ammonia as stated above. (2) The pro- 

 duction of hydrocyanic acid from formaldehyde through 

 formic acid, ammonivim formate, and formamide ; and, in the 

 same way, we have the passage of aldehydes in general 

 through their acid-amides to nitrils, which is the view held 

 by Laurent and Marclial. (3) From the interaction of 

 ammonia, hydrocyanic acid or the nitrils, and the various 

 aldehydes can be produced all the known amino-acids, and 

 hence the synthesis of proteins. 



I wish, in conclusion, to express my indebtedness to Pro- 

 fessor Anderson Stuart for affording every convenience in 

 the laboratory to the carrying out of this work. 



* Annal. Jard. Roh Buit. 1895. 

 t Gazzetti, 37, 1907, 586. 



