STREPTOCOCCUS HEMOLYTICUS 163 



and protein splitting by bacteria, whereas measurement of the 

 hydrogen-ion concentration in cultures measures the resultant of 

 both these actions. 



It seemed advisable at the beginning of the present phase of the 

 investigation to obtain information as to the level of final acidity 

 produced by Streptococcus hemolyticus in broth media contain- 

 ing a number of the common fermentable substances employed 

 in the bacteriological laboratory. Accordingly experiment I was 

 carried out. 



Methods and technic 



Culture. All of the work to be described in the present paper 

 was carried out on one pure strain of Streptococcus hemolyticus^ 

 This strain, designated as the "H," was originally isolated from 

 the lung in a fatal case of bronchopneumonia complicated by 

 endocarditis, and corresponds to culture number 136 in the series 

 obtained during the investigation of pneumonia in military 

 camps by the Rockefeller Commission. The ''H" strain was 

 of high virulence, owing to repeated passage through rabbits 

 in an investigation of experimental streptococcus empyema, and 

 the pleural fluids of such animals, taken at autopsy with sterile 

 precautions (Gay and Stone, 1920), were found to serve as an 

 excellent source of culture material. All pleural fluids were 

 stored in the ice chest as the contained organisms have been 

 found to remain viable under such conditions for a number of 

 weeks. A transplant of 0.2 cc. of the pleuritic exudate was made 

 into 5 cc. of 1 per cent glucose broth and the tube incubated for 

 eighteen hours. As this first generation culture invariably con- 

 tained a considerable amount of cellular debris, a second sub- 

 culture was prepared in a similar manner. This second genera- 

 tion served as a source of inoculum in practically all of the 

 experiments to be described. The eighteen-hour incubation 

 period was chosen inasmuch as preliminary tests had shown 

 that rapid growth nearly always obtained in sub-cultures pre- 

 pared from a parent culture of this age. 



Culture media. Beef infusion broth served as the basis of 

 the media employed throughout the work as it is a generally 



