20 



SELMAN A. WAKSMAN 



see from the following experiment, where to the synthetic media 

 previously used 3 per cent of glucose was added in place of 

 glycerol (nitrogen source 0.2 per cent). 



Most of the species tested made a better growth with glucose 

 as a source of carbon than with glycerol, using ammonium salts 

 and urea as sources of nitrogen. The poorest growth was ob- 

 tained with ammonium sulfate, due to the fact that the reaction 

 soon became distinctly acid with this source of nitrogen, the 

 pH values changing from 5.8 to 4.6 and even 4.2 which is a 

 limiting reaction for the growth of actinomycetes, as will be 

 shown in the following paper. 



TABLE 4 

 The utilization of ammonium salts and urea as sources of nitrogen of actinomy- 

 cetes, with glucose as a source of carbon 



To test further the utilization of nitrites, different concentra- 

 tions of this salt were added in place of the nitrate to the syn- 

 thetic solution containing either glucose or glycerol as a source 

 of carbon. The results are recorded in table 5. 



It is obvious that the actinomycetes can assimilate nitrites 

 readily, when these are present in small enough amounts not to 

 exert any toxic effect. In the presence of only 50 mgm. of 

 NaN(>2 per 1000 cc. of medium, all the species tested produced 

 a fair to good growth with both glucose and glycerol as sources 

 of carbon. With the increase of the nitrite content, the growth 

 increases, due to the larger amount of available nitrogen, but 



