STREPTOCOCCUS HEMOLYTICUS 187 



the outset and at two-hour intervals by removing aseptically 2 

 cc. of material from the flasks. The experiment continued 

 through twelve hours, at the conclusion of which period both 

 cultures had reached their characteristic final level of Ph. 



The outstanding fact here, as may readily be seen by reference 

 to the curves (fig. 5), is a more rapid attainment of high levels of 

 acidity on the part of the culture containing horse serum. 

 Though a stationary period of two hours is noted in each, the 

 lag in the glucose culture is of two hours longer duration than in 

 the glucose-serum culture. A close parallelism in rates is seen 

 during the maximum period. 



It would seem logical to expect that the differences manifest 

 in the above experiment would be closely correlated with the 

 rates of increase in numbers of cells in the two cultures; in other 

 words, multiplication at a maximum rate would be initiated 

 earher in the serum-glucose medium. It is a well recognized 

 fact that we have at our disposal no very satisfactory method 

 of enumerating viable streptococci. The method of Wright, 

 though useful in the standardization of bacterial vaccines, gives 

 only approximate results, and moreover, furnishes values which 

 represent the total organisms, viable and nonviable, present in 

 a culture. On the other hand, the method of plating dilutions 

 of a culture which is recognized as valuable in numerical deter- 

 minations of such organisms as Bad. coli and Bad. typhosum, 

 is not adequate for enumerations of streptococci owing to the 

 fact that single colonies upon the plate almost invariably repre- 

 sent streptococcal chains of varying length. Moreover, there 

 arises a possibility of the breaking up of coccal chains through 

 the mechanical disturbance occasioned in preparing dilutions of 

 the culture. 



Though the inadequacies of these two procedures were recog- 

 nized it was nevertheless considered advisable to repeat experi- 

 ment VIII supplementing the Ph determinations at two-hour 

 intervals with estimations of the number of viable organisms 

 through the medium of plate counts. 



