EXPERIMENT STATION BULLETINS. 



481 



is easily explained by the very probable assumption that certain nitro- 

 gen atoms can be split off from the peptone molecule by hydrolysis, i. e. 

 without simultaneous iorniation of COo, while the bulk is liberated only 

 if the adhering organic radicals are oxidized. 



III. EXPERIMENTS WITH OTHER AEROBIC BACTERIA. 



The experiments in the preceding pages have been carried on exclus- 

 ivel}' with bacteria liberating ammonia from peptone which was found 

 to be a process of complete oxidation. It is probable that other strictly 

 aerobic bacteria will behave similarly in soil, because with them, also, 

 the oxygen supply is the regulating factor. Bacteria requiring much 

 oxygen, such as the vinegar bacteria, require a very thin moisture film 

 to accelerate the oxygen exchange as much as possible. The bacteria 

 which require oxygen for their energy supply will all belong to this 

 group. But there are other aerobic bacteria obtaining their energy from 

 nonoxidative processes, and requiring oxj-gen for life, such as the urea- 

 fermenting organisms. The amount of oxygen used by these organisms 

 is very small, and the replacement of oxygen will be much less im- 

 portant to them than to the vinegar bacteria. Bacteria of this type 

 should hardly be influenced at all by the ventilation and by the presence 

 of sand and the exposed surface, except that too thin a moisture film 

 must prevent the ready food supply, and consequently retard the en- 

 tire metabolism. The following pages give three examples of aerobic 

 bacteria acting upon various compounds. 



Azotohacter in Sand and Solution. — The Azotohactor species are 

 know as strictly aerobic bacteria. Krainsky* detennined the amount 

 of COo produced by a pure culture of Azotohacter in sand with 5, 15 and 

 20% moisture. He computed his data per 500 g. of sand, but he com- 

 pares mainly the relation of CO, to the amount of nitrogen fixed. 

 From his data can be compiled the following table: 



TABLE XIV. 

 Azotohacter in Mannit-Solution + Sand. {All data per 100 cc. of Solution.) 



The nitrogen fixed by young cultures of Azotohacter may be consid- 

 ered proportionate to the number of cells. Under this supposition, it 

 can be stated that the bacteria grew best at 5% moisture, and used the 

 carbon source most economically. Since Krainsky does not mention 

 the grainsize of the sand, it is not possible to make any computations 

 concerning the moisture film. Nothing can be said even concerning the 

 optimum moisture because there are no data to fill the gap between 5 

 and 15% moisture. 



One little experiment concerning the nitrogen fixation of an Azo- 



*Centralbl. f. Bakt. II, Bd. 26 (109) p-231. 

 61 



