METABOLISM OF ACTINOMYCETES 33 



Hoagland (1918) stated that nutrient solutions with an acid 

 reaction reach an approximately neutral reaction after contact 

 with plant roots for various periods of time. Gainey (1918) has 

 shown that the occurrence of Azotobacter in the soil depends 

 on the hydrogen-ion concentration of the soil, the organisms being 

 present when the concentration of the hydrogen-ion is not more 

 than 10~ 6 (pH value not less than 6.0). Waksman (1918) con- 

 firmed these observations by showing that cranberry soils having 

 an hydrogen-ion concentration of more than 10~ 6 (pH 6.0) do 

 not contain any Azotobacter cells. Fred and Loomis (1917) 

 found that alfalfa bacteria bring about changes in the reaction of 

 the medium which are favorable for their reproduction. 



Miinter (1913) reported that actinomycetes are very suscep- 

 tible to acids. Lutman and Cunningham (1914) have shown that 

 A. scabies produces no acid, or only very seldom produces any 

 acid, on organic media; the best growth of this organism is ob- 

 tained in slightly acid or neutral media; the organism is quite 

 sensitive to larger quantities of either acids or alkalies. 



Gillespie (1918) has shown that there is a limiting acidity (as 

 measured by the hydrogen-ion concentration) for the growth of 

 A. scabies (chrome-genus); the limiting exponent (pH value) is 

 between 4.8 and 5.2; the organisms will grow at a reaction having 

 a higher exponent, but not a lower; the growth is accompanied 

 by a marked decrease of acidity and the manner of growth gives 

 reason to doubt whether more than a poor growth can occur at 

 the limiting exponent. 



The investigations reported in the following paper will deal 

 with the changes in reaction of the culture medium as affected by 

 the growth of actinomycetes as well as the effect of the initial 

 reaction of the medium upon the growth of these organisms. 



The medium used most extensively in previous investigations, 

 namely a modified Czapek's solution, was also used in this work. 

 To a liter of distilled water containing 1 gram K 2 HP0 4 , 0.5 gram 

 MgS0 4 , 0.5 gram KC1, 0.01 gram FeS0 4 , were added the different 

 carbon and nitrogen compounds. The solutions were distrib- 

 uted in tubes (or Erlenmeyer flasks), plugged with cotton and 

 sterilized at 15 pounds steam pressure for fifteen minutes. The 



THE JOUBNAL OF BACTERIOLOGY, VOL. 5, NO. 1 



