GROWTH OF CERTAIN ANAEROBES 



421 



centration. All sets of nine tubes, except one intended to serve 

 as a control for the pH determination, were inoculated with the 

 same amount of bacterial suspensions. Simultaneously there 

 were added a few milligrams of solid calcium sulphide powder. 

 The microorganisms were taken from a twentj^^-hour pepton- 

 gelatin culture. Before inoculation all tubes were heated to 

 about 37°. 



TABLE 1 



Composition of "Standard" broth media 



30 cc.- broth, HCl, NaOH, or H2O, 32 cc. 



The tubes were placed in an incubator at 37° and after cer- 

 tain intervals growth was recorded. No microscopic count of 

 the bacilli was made, the growth was merely estimated, and in 

 order to be able to reproduce the results graphically we have 

 indicated the amount of growth by numbers from to 4. Pre- 

 liminary experiments indicated that a time of incubation of 

 from fifteen to twenty hours was the most favorable to determine 

 the optimal growth. 



The initial and the final pH values were determined according 

 to Clark and Lubs, with the method described in the mentioned 

 paper by Dernby and Avery. All our experiments showed that 

 under the chosen conditions (see tables 2 and 3) these anaerobes 

 did not (at least during the first days of incubation) change the 

 hydrogen ion concentration of the medium to any appreciable 

 extent. Therefore it was not necessary here as in the case with 

 pneumococcus or diphtheria bacillus to add any buffers. From 



