METABOLISM OF ACTINOMYCETES 43 



different reaction. When the utilization and splitting of the 

 gelatin in the absence and presence of starch are studied (data 

 reported in paper III of series), we find that, in the presence of 

 starch, the gelatin was often attacked to a lesser extent than 

 in the absence of starch and since the reaction in that case was 

 usually more acid, we can conclude that the alkalinity is produced 

 as a result of the splitting of the gelatin molecules and a greater 

 acidity is due not to the production of acid from the starch, but 

 to the smaller amount of gelatin split. The available carbo- 

 hydrate thus exerts a protective action upon the protein (selec- 

 tive metabolism) as in the case of bacteria and molds, and the 

 difference in reaction in this instance is due to the difference in 

 the nitrogen and carbon metabolism of the organism. 



To study further the effect of an available carbohydrate upon 

 the change in hydrogen-ion concentration of protein media as a 

 result of the growth of actinomycetes and compare it with the 

 effect produced upon bacteria, the following experiment was 

 outlined. Plain bouillon was made up according to the routine 

 bacteriological methods and divided into 2 portions; 1 per cent 

 glucose was added to one portion, but not to the other. The 

 media were tubed and sterilized, then incubated with a known 

 acid producing bacterium (B. coli), a known protein splitting 

 bacterium (B. proteus), a common mold (Aspergillus niger) and 

 several actinomycetes. The cultures were incubated at 37° and, 

 at the end of three and seven days, the reaction was determined. 



B. coli, in the absence of glucose, changed the reaction at first 

 to slightly acid (acting probably on the sugar present in the 

 meat infusion), but soon turned it to alkaline; in the presence of 

 glucose, the medium changed to a distinct acid, the acidity in- 

 creasing with the period of incubation. B. proteus changed the 

 medium, free from glucose, to a distinct alkaline and, in the pres- 

 ence of glucose, to a distinct acid. Aspergillus niger, which 

 rapidly attacks both proteins and carbohydrates left the glu- 

 cose-free and the glucose media more alkaline than did both 

 bacteria, also, however, producing a distinct acidity in the 

 glucose medium. The actinomycetes changed the glucose-free 

 medium in nearly all cases to alkaline (except A. poolensis) and 



