METABOLISM OF ACTINOMYCETES 41 



was left unadjusted; glucose broth containing 1 per cent peptone, 

 0.5 per cent Liebig's meat extract, 0.5 per cent of NaCl and 1 

 per cent of glucose, reaction adjusted to pH 8.0; milk to which 

 brom cresol purple was added as an indicator, as suggested by 

 Clark and Lubs (1917). The gelatin cultures were incubated at 

 18° for thirty-five days and pH determinations made on the 

 liquefied portion of the gelatin; the glucose broth cultures were 

 incubated at 25° for 15 days and the milk at 37° for fifteen to 

 twenty days. No pH determination could be made with the 

 milk cultures, for very obvious reasons, but the change in reac- 

 tion was designated as follows: no change, -f- faint alkalinity, 

 + + fair, + + + good, + + + + highest alkalinity. 



The data presented in table 4 again bear out the fact that an 

 Actinomyces may produce acid in one medium, while another 

 medium will be made alkaline; the change in reaction seems to 

 depend entirely on the source of nitrogen. While there was 

 usually very little difference between the gelatin cultures contain- 

 ing starch and those not containing any available carbohydrate, 

 the difference between the change in reaction produced in gela- 

 tin, glucose broth and the milk was often quite distinct. In sev- 

 eral cases the organisms acted alike on all media: A. violaceus- 

 ruber, A. poolensis, 96, A. griseus, 206, 161, and others left all 

 the media distinctly alkaline; A. scabies, which, as was pointed 

 out in table 2, has a tendency to turn the medium always alka- 

 line behaved in a similar way in these experiments. A. reti- 

 culus-ruber, 145, and 154 left all the media distinctly acid (milk 

 unchanged, gelatin changed from acid to slightly less acid). 

 Other organisms, however, such as A. lavendulae, A. exfoliatus, 

 A. alboflavus, A. albosporeus and others changed one medium to 

 acid and another medium to alkaline. 



The addition of 1 per cent starch to the gelatin had, in most 

 instances, no effect on the change of reaction and even resulted 

 in few cases in a more alkaline reaction (A. scabies, A. pheochro- 

 mogenus, A. rutgersensis) , although, where there was a change in 

 reaction, it was usually towards acidity. The addition of starch 

 resulted in a number of cases in leaving the medium more acid 

 (lower pH value or greater hydrogen-ion concentrations are 



