356 AUGUSTO BONAZZI 



the formation of nitrites as is shown in table 14." By refer- 

 ring to table 14 of this author we find that 18.9 mgm. of nitrate 

 nitrogen were lost with a resulting ''slight" reaction for nitrites in 

 the solution. A concentration of 18.9 mgm. of nitrites in 100 cc. 

 of solution (for that matter even much less than this) gives more 

 than a ''sHght" reaction with such a sensitive reagent as the 

 Tromsdorff solution, and it is more than questionable if the 

 totality of the nitrate lost is to be found in the form of nitrites. 

 In addition the analytical data point to the incorrectness of this 

 view. 



It is a common experience to see a good development of Azoto- 

 bacter in cultures containing nitrates while poor development 

 takes place in cultures containing no nitrate. For the sake of 

 argument we may assume that the nitrate acts solely in virtue 

 of the stimulation it is supposed to exercise on the nitrogen 

 fixing power of the organism. This increase in the nitrogen 

 fixing power, if present at all, is relatively small and amounts to 

 only 200 to 500 per cent of the original fixation; a stimulation 

 that, when we consider the small original fixation, is relatively 

 small. Although actual data are wanting, we may assume this 

 stimulation to amount to 500 per cent (see the data of Hills on 

 the influence of nitrates on the nitrogen fixation in sterilized 

 soils). A relative increase of 500 per cent in nitrogen fixation 

 brought about by an increase in the number of active cells of 

 3150 per cent represents an inconceivable stimulation in the 

 fixation of nitrogen, every cell actually fixing less nitrogen in 

 presence than in absence of the fixed nitrogen. It must further- 

 more be admitted that such a nitrate addition stimulates growth 

 in a different measure than it does nitrogen fixation. Here again 

 we obtain proof of the fact that the nitrogen fixing capacity of 

 the cell is not intimately connected with the function of growth 

 and reproduction. 



If the stimulation hypothesis is to be accepted how are we 

 to consider such a difference in these two powers? We are in 

 reality more justified in considering the nitrates as stimulating 

 (or better still aiding) growth in the first place. Basing our 

 working hypothesis on the physiology of the organism we see 



