168 LAURENCE F. FOSTER 



final Ph. In the work of the same investigators (1919a) upon 

 Streptococci of human and bovine origin it was shown that the 

 same final Ph is reached in broth containing 0.5, 1, or 1.5 per 

 cent of glucose. Sekiguchi (1917) found the highest production 

 of acid by streptococci with 0.5 to 2 per cent of glucose. Amounts 

 of sugar over 5 per cent caused reduction in acid formation 

 though growth was not hindered. H. Jones (1920) has recently 

 found that a number of organisms are able to produce their 

 characteristic final hydrogen-ion concentration provided 0.2 

 per cent or more glucose be present in the medium. He failed 

 to state the initial Ph of the medium which factor has an impor- 

 tant bearing on the minimum concentration of a sugar needed 

 for production of the final acidity by any given organism. The 

 effect of varying amounts of xylose upon the production of 

 volatile acid by xylose fermenting organisms has been studied 

 by Fred, Peterson, and Davenport (1919) who found that 2 

 per cent of the sugar gave the maximum production of acid. 

 The presence in the culture medium of substances which through 

 their buffer effect have the power of neutraHzing some of the 

 acid as it is produced is of interest and importance in this 

 connection. 



Henderson and Webster (1907) in 1907 suggested the use of 

 phosphates to preserve neutrahty in media during the growth of 

 acid- or alkah-forming organisms, and Clark (1915a) has more 

 recently pointed out in considerable detail the great importance 

 of properly buffered media in bacteriological work. Using lots 

 of broth containing different buffers, Clark (1915b) showed that 

 Bad. coll produces somewhat lower levels of Ph in the more 

 highly buffered media. 



KHgler (1916) working with cultures of Bad. doacae, Bad. 

 aerogenes, and Bad. coli studied the final Ph as influenced by 

 different concentrations of peptone, Na2HP04, and glucose. 

 The concentration of peptone was found to influence the utiliza- 

 tion of glucose by the organisms in such a way as to result in a 

 lower final Ph with a low peptone concentration in the medium. 

 In some cases the presence of buffer allowed all of the sugar to 

 be used up with a subsequent rise of Ph thus indicating that an 



