84 ABSTRACTS 



ably ranging from a few hundred to several thousand per cubic centi- 

 meter. In the certified milk they were about in the same proportion as 

 in the pasteurized samples. From one dairy in 16 specimens of milk no 

 hemolysing streptococci were found. In all others some were found. 



A study of these 85 strains of hemolysing streptococci was made 

 as regards their morphology, cultural characteristics and certain other 

 properties. They vary considerably among themselves. They are 

 more resistant to heat than human strains of hemolytic streptococci. 

 They possess little or no virulence for rabbits ; therefore in all probability 

 not for man. They rapidly acidify and coagulate milk and grow well 

 at 20°C. They may form short or long chains but as seen in milk they 

 often appear in pairs or a chain of few elements. While they are all 

 definitely hemolytic (type B, Theobald Smith) the characteristics of 

 the hemolytic zone on plates may vary in certain respects. 



These milk strains are different from certain strains of hemolytic 

 streptococci found at times in diseased udders in cows. These latter 

 resemble the strains of hemolytic streptococci from human sources 

 and are virulent for rabbits. 



There is no reason to consider that these milk strains have any 

 sanitary significance. The importance however of certain strains of 

 hemolytic streptococci in relation to epidemics of sore throat makes 

 it necessary to study carefully all such organisms in milk. 



By itself the hemolytic property has no more value for identification 

 purposes than many other characteristics and perhaps less than some. 

 But it is of great importance on account of the practical value of the 

 blood agar plate method as a means of initial separation of hemolytic 

 strains from the many strains of non-hemolytic and feebly hemolytic 

 streptococci found in milk. 



Hydrogen-ion Concentrations in Cultures of Streptococci. S. Henry 



Ayers. 



Hydrogen-ion concentrations were determined in cultures of strepto- 

 cocci from the following sources: 34 from various human infections, 18 

 from the human mouth, 89 from milk and 60 from the udder, feces and 

 mouth of the cow, making a total of 201 cultures. 



The cultures were grown in a broth containing 1 per cent cerevisine 

 (a dry-yeast preparation), 1 per cent peptone, 1 per cent of the test 

 substance, and distilled water. All the streptococci grew well in this 

 medium and it does not contain a fermentable sugar. Many of the 

 cultures would not grow in extract broth or in infusion broth when the 

 muscle sugar was removed by fermentation with B. coli. 



Since the acidity may be defined in terms of hydrogen-ion concen- 

 tration this was determined instead of the titrable acidity. The 

 test substances used were glucose, lactose, and cane sugar, raffinose, 

 mannite and inulin, and the hydrogen-ion concentrations were de- 

 termined by a colorimetric method. 



The hydrogen-ion concentration can be represented by the symbol 

 P+H and on this basis the neutral point of absolutely pure water is 



