STUDIES ON AZOTOBACTER CHROOCOCCUM BEIJ. 



357 



that the nitrates increase growth of the cells and their multipli- 

 cation with a corresponding increase in sugar consumption, and 

 in this process the nitrates disappear to be later found in the 

 organic form, and only after such a phenomenon has taken 

 place does the atmospheric nitrogen fixation really become 

 active. 



Experiment 27. Fifty cubic centimeter portions of a solution 

 of the following composition were placed into 500 cc. Kjeldahl 

 flasks together with 0.1 gram CaCOs. 



Mannitol 



MgS04 + 7H2O 



NaCl 



CaS04 + 7H20. 

 K2HPO4 



20.0 grams 

 0.408 gram 

 0.200 gram 

 0.127 gram 

 0.200 gram 



Tap water 1000.00 cc. 



TABLE 18 



Nitrogen fixation by Azotobacter in presence and absence of nitrates 



TREATMENT 



None: 



Cheek 



. Check 



Inoculated. 



Inoculated. 

 Nitrate: 



Check 



Check 



Inoculated. 



Inoculated. 



Inoculated. 



Inoculated. 



Inoculated. 



NITROGEN 

 FIXED 



+0.81 



■0.97 



* Determination lost. 



Eleven flasks were prepared and numbered successively from 

 1 to 11. They were arranged as follows: Nos. 1^ inclusive 

 received in addition to the above solution 5 cc. of water and 

 flasks 5-11 inclusive received 5 cc. of a 0.843 per cent solution of 

 Ca(N03)2 + 4H2O. All the flasks except nos. 1, 2, 5, 6 were 



