498 AUGUSTO BONAZZI 



The results obtained by the use of ammonium carbonate as 

 a source of nitrogen and carbon, as well as those obtained with 

 a non-carbonated base emphasize the fact that it is the free 

 CO2 that is utilized by the cells, a view substantially corrobo- 

 rated by the findings of Ashby and of Hopkins and Whiting 

 reported above. 



This free carbon dioxide is not necessary for the formation of 

 ammonium carbonate, but for another purpose : chemosynthesis. 



The oxidation of ammonia is to be considered as taking place 

 in two steps : (a) one of respiration with resultant gain in energy 

 and synchronous nitrogen absorption, (b) the other of nitrogen 

 assimilation (nitrification proper) whereby oxidation of the ab- 

 sorbed nitrogen takes place, the utiUzed portion going to make up 

 the following cell generations, nitrous acid is split off and excreted 

 as a non-utilizable product, and energy is liberated. There- 

 fore, if the free carbon dioxide were removed from a culture 

 containing both ammonium carbonate, as a nitrogenous source, 

 and large numbers of bacterial cells, respiration should be great 

 enough to allow some nitrification to take place. If, on the 

 other hand, the number of active cells were Umited, nitrification 

 would come to a standstill before a quantity of nitrites were 

 formed detectable by the ordinary chemical means. Experimen- 

 tal evidence bears proof of the correctness of the above 

 hypothesis. 



SUMMARY 



This paper reports a study of the functions of autotrophic 

 carbon assimilation and nitrogen nutrition of the nitrosoferment. 

 These functions are found to be intimately connected and mutu- 

 ally interdependent, the bacterial cell being unable to assimilate 

 the abundant stores of nitrogen in a nutritive solution in the 

 absence of *'free" carbon dioxide, even though a carbonate 

 as such, be present, in the medium. Consequently on the 

 presence of this ''free" carbon dioxide is dependent the process 



present author found nitrification to proceed when the tube containing concen- 

 trated KOH was placed very near the mouth of the flask so that free circulation 

 of the air was interfered with. 



