30 



in nitrogen-poor media, flasks were filled with Ashby's medium 

 as before, one gram of urea introduced, and inoculated 

 as in the nitrogenous medium. After forty eight hours the 

 surface was covered with gas bubbles and on the fourth day 

 a strong odor of ammonia was evolved from each flask. It 

 therefore appears that in the presence of an abundant nitrogen 

 supply urea is converted into ammonium carbonate, and that 

 this process is not impeded by the presence of carbohydrate 

 in great excess, but is rather promoted, even though the 

 nitrogen content be very small. 



Several flasks of Ashby's medium were inoculated with 

 soils and thio-urea introduced in place of urea. The growth 

 in these flasks was much less pronounced than in those con- 

 taining urea. Evidently ammonium sulphite was not formed. 



Hippuric acid is split, in nitrogenous media, into benzoic 

 acid and amino-acetic acid. Several flasks of Ashby's medium 

 were inoculated with soil and one gram of hippuric acid in- 

 troduced. After a few days the surface was overgrown with 

 molds, later a vigorous evolution of carbon dioxide was per- 

 ceptible, the overlying growth being forced high in the flask. 

 In a second experiment the hippuric acid was neutralized with 

 sodium hydroxide before being transferred to the Ashby's 

 medium. The splitting of the hippuric acid molecule into 

 benzoic acid and amino-acetic acid, and the subsequent union 

 of the benzoic acid and calcium carbonate to form calcium 

 benzoate, necessitates the liberation of considerable quanti- 

 ties of carbon dioxide. Amino-acetic acid (Glycocoll) is 

 reduced by soil bacteria to ammonia and acetic acid, this re- 

 duction is consummated both in nitrogenous and non-nitro- 

 genous media. 



THE REDUCTION OF NITRATES TO NITRITES 



The breaking down of organic compounds by bacterial 

 agency, falls under two categories; simple cleavage, and partial 

 elementary disintegration of the proteid and carbohydrate 

 molecule. In the first category we are concerned with the 

 simple splitting off of groups from the original relatively com- 

 plex molecule. Among the cleavage products may be men- 

 tioned alcohols, esters, mercaptans, amino-acids, phenol, 



