STREPTOCOCCUS HEMOLYTICUS 



183 



Experiment VII . The relation of the age of parent culture to the 

 rate of acid formation in glucose broth 



Four cultures of Streptococcus hemolyticus were made in the usual 

 manner at intervals of six hours. After eighteen hours incubation 

 sub-cultures were made and these second-generation cultures incu- 

 bated. The schedule was so arranged that at the time of the 

 final inoculation into the medium of the experiment (20 cc. por- 

 tions of 1 per cent glucose broth) organisms would be taken from 

 parent cultures of six, twelve, eighteen and twenty-four-hours 

 age. One hour previous to the final seeding counts of each 

 parent culture were made by the method of Wright in order 

 that each tube of broth to be used in the experiment might 

 receive approximately the same number of organisms. The 

 inoculum was based upon the proportion, 0.8 cc. of a twenty- 

 four-hour culture per 20 cc. of broth. 



Bacterial counts 



Examination of the curves (fig. 4) shows that (2) (from twelve 

 hour culture) reaches the characteristic final Ph earliest, then 

 come in order the tubes from the six-, eighteen- and twenty-four- 

 hour parent cultures. The onset of the maximum period is seen 

 to follow the same order. As might be expected, the differences 

 are shown almost entirely in the duration of the lag and station- 

 ary periods of the four cultures. It is a fact of interest and 

 importance that the rates of acid formation during the maximum 

 period (table 6) were practically equal in the four cases. 



From a consideration of the work of various investigators 

 upon the life phases of an organism the results obtained here are 

 not unexpected. It has been repeatedly demonstrated that the 

 maximum rate of acid formation in glucose broth occurs between 



JOURNAL OF BACTERIOLOGY, VOL. VI, NO. 2 



