36 SELMAN A. WAKSMAN AND JACOB S. JOFFE 



forth in table 2. If the alkalinity of the medium is due to the 

 utilization of the nitrate-ion, while the sodium ion is left in the 

 medium, the same should hold true when NaN0 2 is present as 

 the only source of nitrogen ; here the nitrite ion would be removed 

 from the medium as the source of nitrogen. But just the oppo- 

 site holds true, the nitrite solution becoming in nearly all cases 

 more acid. We must look, therefore, for the difference in change 

 of reaction not to the using up of the acid ion by the organism, 

 but to another factor. It is a commonly accepted fact that the 

 addition of NaN0 3 , as a fertilizer, to the soil will leave the soil 

 more alkaline, and the tendency is to suggest the previous ex- 

 planation. But the fact has not been established as yet whether 

 the NaN0 3 is assimilated by the plants and microorganisms as 

 such or only in the form of ions ; in the latter case the explanation 

 would stand. It cannot, however, explain the difference in be- 

 havior of the same organisms upon NaN0 3 and NaN0 2 by which 

 the first medium is left alkaline and the second acid. 



It was pointed out in paper II of this series that the change 

 of reaction towards alkaline usually coincided with the amount 

 of growth of a particular species and the nitrate reduction. Those 

 sources of carbon which offered a better source of energy would 

 allow a greater change in reaction which would be accompanied 

 in many cases by the presence of larger quantities of nitrites. In 

 the process of reduction of a nitrate to a nitrite molecule, one 

 atom of oxygen is split off and this may either combine with one 

 atom of hydrogen producing an hydroxyl ion (which may not be 

 possible at all) or with a molecule of hydrogen giving a molecule 

 of water. In either case the hydrogen tension of the medium 

 would be reduced which would explain the decrease of the hydro- 

 gen ion concentration of the medium or increase in alkalinity, in 

 the case of the nitrate, but not of the nitrite medium. 



The following experiments were carried out, with the purpose 

 of finding the effect of the source of nitrogen upon the change in 

 reaction; 30 grams of glycerol were used in all cases as a source 

 of carbon, and 2 to 5 grams of each source of nitrogen per liter. 

 Glycerol was used in this last series, since it proved to be a favor- 

 able source of carbon for nearly all actinomycetes, and since it 



