162 J. M. SHERMAN AND W. R. ALBUS 



FERMENTATIVE CHARACTERISTICS 



The value of fermentation tests with carbohydrates and 

 related compounds in systematic bacteriology has become well 

 established. The fermentative characteristics have been made 

 use of especially in studies on streptococci, and by their means 

 this very evasive group has been subdivided into a number of 

 fairly well defined types. These tests have not been used, 

 successfully at least, to distinguish between streptococci of the 

 pyogenic and lactic-acid types. 



In this study glucose, galactose, levulose, maltose, lactose, 

 sucrose, raffinose, dextrin, inulin, starch, glycerine, mannit and 

 salicin were used. The medium used for the fermentation 

 tests had the following composition: 



ptr cent 



Beef extract 0.3 



Peptone 1.0 



Dibasic potassium phosphate 0.5 



Test substance 1.0 



In the tests made with glucose, galactose, levulose and maltose 

 the dibasic potassium phosphate was omitted. 



In making the tests the cultures were incubated at 33°C. 

 and then titrated against 2^0 NaOH, with phenolphthalein as 

 indicator, and the results expressed as per cent of normal acid. 

 An increase above the control tube of 1 per cent normal acid 

 was regarded as a positive test for fermentation. The sugars 

 were incubated seven days and the other compounds two weeks 

 before titration. In cases in which less than 25 per cent of the 

 organisms were either positive or negative the minority cultures 

 were retested. The results of this study are summarized in 

 table 3. 



A review of these data shows that the fermentative properties 

 of the two groups are, generally speaking, quite similar. Al- 

 though resembling each other on the whole, a very noticeable 

 break in the similarity is found in the case of sucrose. It is seen 

 that 76 per cent of the udder organisms attacked this substance 

 as against only 6 per cent of the other group. The fermentative 

 powers of the cultures are presented graphically in figure 3. 



