EXPERIMENT STATION BULLETINS. 



483 



moisture is at the height of its acidity, while the sand with 20% mois- 

 ture is just getting started. The actual efficiency of these bacteria 

 can be estimated only if CO. and CH;,CO,.H are both determined. 



It would be absolutely wrong to conclude from the above table 

 that the optimum conditions prevail at 20 — 30% moisture. One 

 should rather conclude that under these conditions the oxygen supply 

 is not sufficient to allow com])lete oxidation of the food, and therefore, 

 the acetic acid accumulates. This is the ideal condition for the vinegar 

 manufacturer, but not for the bacteria themselves. They would be much 

 better off if they could dispose of the noxious acid by changing it into 

 the volatile carbon dioxide. For such oxidation, the sand cultures with 

 5 and 10% moisture afford much better opportunity. 



Urea Bacteria in &and and Solution. — The urea-fermenting bacteria 

 differ from the previously mentioned bacteria by the circumstance that 

 they can provide for their energy by hydrolysis, without using oxygen. 

 However, thev are aerobic bacteria and cannot live in the entire ab- 

 sence of oxj^gen. They need the oxygen probably for some process 

 in cell construction, and this amount is so small that for some time, 

 they were considered to be facultative anaerobic. 



The arrangement of the experiment was similar to the preceding. The 

 nutrient medium was a solution of 5% of urea and 0.2% of citric acid. 

 To 1.5 liters of this was added 20 cc. of bouillon. The culture used 

 which was not pure, was obtained by [Ritting soil into a little of the 

 above solution until fermentation started, and then transferring several 

 times in the same medium. The urea solution was inoculated heavily 

 with this culture containing an accumulation of bacteria. The medium 

 was then transferred b}^ means of sterile pipettes into flasks containing 

 each 100 g. of sterile sand. The ammonium carbonate was determined 

 by diluting and titrating aliquot portions with tenth normal acid 

 and methyl orange. The experiment was carried out by Mr. H. K. 

 Wright. 



TABLE XVII. 

 Urea Fermentation in Sand and Solution. 

 (Per cents of (NH4)2C0 3 per 100 cc. of solution.) 



The agreement of the data is not satisfactory because of the inac- 

 curate method of analysis and of the evaporation of ammonia in the 

 drier samples. Perhaps the fact that no pure culture was used, also 

 influenced the results. It can be concluded with certaintv, however, 

 that the optimum conditions are not at 10% moisture, but over 20%. 



