METABOLISM OF ACTINOMYCETES 47 



3. When ammonium salts of strong acids are present as the 

 only source of nitrogen, the medium tends to become distinctly 

 acid, due to the fact that the cation is used up by the organism 

 and the anion is left in the medium. 



4. With proteins and amino acids the reaction may be un- 

 changed, or may become acid or alkaline, depending on the 

 species, source of carbon and original hydrogen ion concentra- 

 tion of the medium. Certain species seem to change the reac- 

 tion of the protein and amino acid media always to alkaline, 

 others always to acid. Leucin, as the only source of nitrogen, 

 nearly always favors a distinct acidity of the medium. 



5. The presence of an available carbohydrate in a protein 

 medium seems to favor the change of reaction to a more acid 

 one. This is explained by the effect of the carbohydrate upon 

 the nitrogen metabolism of the organisms and not by a direct 

 acid production. 



6. With media of different hydrogen-ion concentrations, the 

 reaction tends to an optimum; the more acid media tend to be- 

 come less acid and the more alkaline media (above the optimum) 

 less alkaline. 



REFERENCES 



Ayers, S. H. 1916 The hydrogen-ion concentration in cultures of streptococci. 

 Jour. Bact,, 1, 84-85. 



Boas, F., and Leberle, H. 1918 Untersuchungen uber Saurebildung bei Pilzen 

 und Hefen. Biochem. Ztschr., 90, 78-95; 92, 170-188. 



Clark, W. M. 1915a The final hydrogen-ion concentrations of cultures of Bacil- 

 lus coli. Jour. Biol. Chem., 22, 87-98. 



Clark, W. M. 1915b The "reaction" of bacteriologic culture media. Jour. Inf. 

 Dis., 17, 109-136. 



Clark, W. M. and Lubs, H. 1917a The colorimetric determination of hydrogen- 

 ion concentration and its applications in bacteriology. Jour. Bact., 

 2, 1-34, 109-136, 191-236. 



Clark, W. M., and Lubs, H. A. 1917b A substitute for litmus for use in milk 

 cultures. Jour. Agr. Res., 10, 105-111. 



Davis, L. 1918 Studies on diphtheria toxin. Jour. Lab. Clin. Med., 3, 358-367. 



Fred, E. B., and Loomis, N. E. 1917 The influence of hydrogen-ion concen- 

 tration of the medium on the reproduction of alfalfa bacteria. Jour. 

 Bact., 2, 629-633. 



Gainey, P. L. 1918 Soil reaction and the growth of Azotobacter. Jour. Agr. 

 Res., 15, 265-422. 



