IDENTITY OF THE LACTIC-ACID STREPTOCOCCUS 



161 



Although these results would appear to indicate that the 

 true lactic-acid organisms as a class are capable of enduring a 

 higher degree of acidity and of producing a more rapid coagu- 

 lation of milk than the pyogenic streptococci, it is desirable to 

 quahfy this conclusion. The manner of securing the lactic 

 streptococci was such as would tend to result in the collection 

 of strains which were especially vigorous in their growth and 

 action on milk. As is well known, the amount of acid produced 



to 



ki 



Qc 



k 



Or 

 a. 



.05 t.O 1.5 



2.0 



PER CENT NORMAL ACID. 



Fig. 2. Frequency Curve Showing Acid Production in Lactose-Peptone- 

 Bile 



in milk is not a very stable character and may be greatly altered 

 by various factors such as, for example, growth on laboratory 

 media. However, the degree of titratable acidity developed is 

 probably of some differential value and it is not unlikely that 

 determinations of actual hydrogen-ion concentrations, such as 

 were made by Clark and Lubs (1915) with the colon-aerogenes 

 bacteria and by Ayers (1915) with pathogenic and non-patho- 

 genic streptococci, would reveal a fundamental difference be- 

 tween these two groups. 



