Chap, hi The construction of Protein 353 



present in the plant, and that the nitric acid so freed is 

 the next step in the construction of protein. He attributed 

 the decomposition to processes in the leaves, as nitrates 

 could be traced towards them in gradually diminishing 

 quantities, but the leaves themselves contained none. He 

 found that crystallizable nitrogenous organic substances 

 are present in leaves, an observation confirmed by several 

 contemporary writers, particularly Biltz, Kellner, and 

 Borodin. 



In 1888 Schimper observed a large formation of calcic 

 oxalate in leaves absorbing much calcium nitrate. He 

 attributed this to the decomposition of the nitrate by the 

 oxalic acid of the plant, thus agreeing with Emmerling. 



Research was followed very soon by speculation, based 

 often upon original observation by the theorists, but some- 

 times traceable to more general grounds. The idea of a 

 reduction of nitrates in the plant had occurred to a few 

 observers before Emmerling had shown how the nitric acid 

 itself might be set free, and the agents of such reduction 

 had been thought possibly to occur among the products 

 of the action of chlorophyll. In 1872 Gautier attributed 

 it to the formaldehyde, whose presence had just previously 

 been suggested by Baeyer. The reduction of nitric acid in 

 light was first actually observed by Laurent in 1890, and 

 later by Berthelot in 1898, and was found to be accom- 

 panied by a production of nitrous acid, nitric peroxide, 

 and oxygen. 



In 1896 Bach put forward a scheme of decomposition 

 to show what the stages of the early decompositions may 

 be, much as Baeyer had shadowed forth the stages of photo- 

 synthesis nearly twenty years earlier. There was at the 

 time very little evidence in support of his speculation, and 

 indeed till the end of the century the hypothesis remained 

 practically unsubstantiated. It served, however, as did 

 Baeyer 's, as a starting-point for research. 



GREEN Z 



