46 SELMAN A. WAKSMAN AND JACOB S. JOFFE 



The same species were also inoculated upon a series of gelatin 

 tubes (15 per cent in distilled water) adjusted to different hy- 

 drogen-ion concentrations. These were incubated at 18 to 20° 

 for thirty days. The reaction of the liquefied portion was then 

 determined, using the phenol-sulphonephthalein series of indi- 

 cators and comparator tubes. The results of these few experiments 

 are given in tables 6 and 7. 



The results reported in the two tables are interesting; they 

 point out clearly how little trust we should lay upon the change 

 of reaction produced in the medium if the initial reaction is not 

 known. It is quite evident that the reaction tends to a final 

 point for most species, this being the optimum reaction for the 

 growth of the actinomycetes, if the initial reaction is not beyond 

 the limits where any growth may take place. When the reac- 

 tion of the medium is too acid it tends to become less acid or 

 more alkaline as a result of the growth of the Actinomyces 

 species; when the reaction of the medium is too alkaline, it 

 tends to become less alkaline as a result of the growth of the 

 organisms. As far as the reaction is concerned, most actino- 

 mycetes are able to develop on the medium for a long period of 

 time since the reaction thus tends to reach an optimum value. 



SUMMARY 



1. The Actinomycetes are not able to produce any appreciable 

 quantities of acid from the carbohydrates studied. The change 

 in reaction of the medium is due to the source of nitrogen. 



2. With different sources of carbon and NaN0 3 as a source of 

 nitrogen the reaction of the medium tends to become alkaline. 

 When NaN0 3 is replaced by NaN0 2 , those organisms that can 

 grow on the latter source of nitrogen, change the medium to acid 

 rather than to alkaline. This difference in behavior of the or- 

 ganism upon those two sources of nitrogen is explained as fol- 

 lows: The Actinomycetes reduce the nitrate to nitrite more or 

 less actively; the oxygen split off from the nitrate molecule is 

 united with the hydrogen or other reducing substances of the 

 medium, thus tending to reduce the hydrogen tension of the 

 medium. 



