soil. PHYSICS, CHEMISTRY AND MICROBIOLOGY 943 



two species, their synergetic activity in the upper strata of the soil results 

 in a harmonious mutual development producing the maxinmm econoni}' 

 in consumption of energetic substances. 



III. Relations between the Fixation of Nitrogen and the Consumption of 

 Non-nitrogenotis Organic Substances by the Nitrogen-fixing Bacteria. — For 

 these investigations, M. Omelianskij used an artificial mixture of Azoto- 

 bacter chroococcum, an aerobic fixer, isolated from the soil of the Institute, 

 and Clostridium Pasteurianum, an anaerobic fixer, isolated from the soils 

 of a kitchen garden in the province of Volhynia, The use of this mixed 

 cultivation was for the same object as in the work last mentioned, a closer 

 approximation to the actual conditions under which the simultaneous 

 activit}' of the nitrogen-fixing microbes takes place in the soil. 



The nutritive medium of this culture was composed as follows per 

 100 cc. : 80 cc. of drinking water, 20 cc. of linseed extract 5 % strength, 

 2 grams of dextrose, o.i gram of potassium phosphate, 0.05 g magnesium 

 sulphate, 0.5 gram calcium carbonate. Dextrose was chosen as a non- 

 nitrogenous substance because it is suitable as a food both for Azotobacter 

 and Clostridium. 



On the 6th April 191 1, this food mixture was poured into 27 Vinograd- 

 ski] flasks at the rate of 100 cubic centimetres to each ; 3 flasks were then 

 left as controls in order to ascertain the quantity of nitrogen and sugar, and 

 24 were sown with the mixture of the two bacteria. During these experi- 

 ments, which lasted 6 weeks, the flasks were maintained at a temperature 

 of 210-220 C. Every 5 days, 3 flasks were taken, in order to determine sugar 

 in one by the Bertrand method, and nitrogen in the two others b}" the 

 Kjeldahl method. 



The principal results of the chemical analyses are grouped in the append- 

 ed diagram, which brings out clearly the most interesting facts ascertain- 

 ed by the researches, namely, the existence of a close relation between the 

 process of assimilation and that of dissassimilation in the cell, which leads 

 to its organic growth. In this diagram, the ordinates exhibit the quantity 

 of nitrogen fixed in milligrams and that of sugar decomposed in grams. The 

 abscissae indicate the duration of the experiments in days. 



On closer examination of the results obtained, it may be said that the 

 process of fixation of nitrogen ran its course uninterrupted!}^ until the avail- 

 able energetic sub.stance was consumed. 



The quantity of nitrogen fixed is relatively small (i-735 mgrms of 

 nitrogen per gram of sugar decomposed), which must be put down to the low 

 degree of activity of the bacterial strains employed in the experiments. 



The curves of nitrogen fixed and sugar decomposed are generall}' 

 parallel. They show a continuous increase throughout the experiment, the 

 maximum rise taking place in the period between the 5tli and 15th day. 



A comparison between the productivity of the work of the bacteria at 

 different periods {of 5 days each) of their life presents some interest. Com- 

 pleting the data of the diagram, it is found that the process of nitrogen 

 fixation is at its best in the first period. The absolute quantity (0.24 mg) 

 of the nitrogen fixed during the first 5 days is insignificant, but relatively 



