40 SELMAN A. WAKSMAN AND JACOB S. JOFFE 



All the species turned the reaction of the medium containing 

 ammonium sulfate more acid and most of them did so also in 

 the media containing the ammonium carbonate, except A. re- 

 ticuli, A. madurae and A. bovis which changed the reaction to 

 alkaline. In the case of urea, we find that all the organisms, 

 with the exception of A. viridochromogenus, caused an increase in 

 the exponent of the medium. This change of reaction is readily 

 explained in the case of the ammonium salts, since the organisms 

 use up the ammonium-ions as a source of nitrogen, leaving the 

 sulfate-ion in the medium and this will tend to make the medium 

 acid. In the case of the three species that changed the reaction 

 of the medium containing the carbonate to alkaline, we assume 

 that perhaps the anion is utilized here as well as the cation. The 

 increase in the value of the exponent in the urea medium is no 

 doubt due to the production of ammonium carbonate out of the 

 urea, while the A . viridichromogenus that changes the reaction of 

 the urea medium to acid made an abundant growth upon the 

 medium and probably used up the alkaline radical. 



The increase in acidity in the ammonium sulfate medium was 

 so great that most species made a very poor growth, because the 

 limiting hydrogen-ion concentration was promptly reached. 



When ammonium salts of organic acids are present in the 

 medium both as sources of nitrogen and carbon, the medium not 

 only does not become more acid, but may become strongly alka- 

 line. When ammonium malate replaces the sucrose and nitrate 

 in the synthetic solution most Actinomyces cultures grow very 

 readily, the reaction of the medium changing in all cases to dis- 

 tinctly alkaline. This is due to the fact that the malate-ion is 

 used as a source of carbon to a much greater extent than the 

 ammonium-ion as a source of nitrogen, since the energy-need of 

 the organism is greater than the nitrogen-need. 



Four liquid media commonly used in bacteriological work were 

 next studied as to their change in reaction resulting from the 

 growth of Actinomycetes. These media were prepared as fol- 

 lows: 15 per cent of Gold Label Gelatin in distilled water as well 

 as 15 per cent of gelatin, with the addition of 1 per cent of starch, 

 were made up in the usual way, tubed and sterilized; the reaction 



