ON NITRIFICATION 495 



It should be assumed, therefore, that the carbon dioxide formed 

 through these reactions can go to replace that removed at the 

 start; the CO2 tension in the liquid and gaseous phase soon 

 approaching that state of equilibrium which is favorable to the 

 action of the nitrite-forming bacteria. In the presence of KOH, 

 or other CO2 absorbent, these reactions are taking place, but the 

 gaseous products formed in relatively small quantities are soon 

 removed by the absorbent, the resulting CO2 tension in the cul- 

 ture solution reaching the point where the normal activity of 

 the organism is impossible. Under such conditions it is even 

 to be doubted whether ammonium carbonate is formed as such 

 and not immediately hydrolyzed and the products of hydrolj^sis 

 distilled from reach of the cells before completion of the synthetic 

 step in the reaction. This is evidenced by the fact that when 

 Omeliansky solution containing aixmionium carbonate as the 

 source of nitrogen is exposed to a concentrated alkaU in a closed 

 system it rapidly changes from an acid reaction, to phenolphtha- 

 lein, to a strongly alkaline reaction. If ammonium sulphate 

 be the source of nitrogen and magnesium carbonate be added to 

 the solution, the final result is the same, a very strong alkalinity 

 being developed where at first only a weak one could be detected. 



In the tables reported above it is evident that such conditions 

 lead to a check on the process of nitrification. The carbonate- 

 carbamate used in view of the hypothesis of Chodat under the 

 above conditions of CO2 removal did not lead to a nitrogen 

 hunger. This is proved by the fact that a solution containing 

 this compound, and incubated in a system in which KOH was 

 present, contained after the incubation considerable quantities of 

 ammonia as determined by the Nessler reagent, while a heavy 

 precipitate was obtained by allowing a drop or two of the culture 

 solution thus incubated to react with Ba (OH) 2. Some carbonate 

 as such was therefore still in solution. 



These last considerations lead to the conclusion that it is the 

 carbon dioxide as such that is necessary to the organisijis of 

 nitrosofermentation and that it can be utilized only when the 

 tension of this gas is above a minimum limit. Thus the nitrogen 

 nutrition of the organism is closely related and in fact completely 



