STREPTOCOCCUS HEMOLYTICUS 177 



If broth containing glucose be inoculated with an actively 

 growing culture of Streptococcus hemolyticus and incubated, 

 there ensue changes in the hydrogen-ion concentration of the 

 medium culminating in the establishment of a limiting or final 

 reaction. A study of these changes, as measured at regular 

 intervals, indicates that the course is a perfectly definite one 

 capable of being separated into the following characteristic 

 phases: (1) Initial stationary period, no change in reaction; 

 (2) latent or lag period, acid formation at a slowly increasing 

 rate; (3) maximum period, acid formation at a constant rate; 

 curve an oblique straight line; (4) period of negative accel- 

 eration, acid formation at a decreasing rate; (5) maximum 

 stationary period, final Ph reached, curve a straight line parallel 

 to the abscissa. 



It will be noted that this sub-division of the course of reaction 

 change corresponds with Buchanan's life phases of a bacterial 

 culture based upon numerical determinations of viable organ- 

 isms, with the exception that his two final periods, representing 

 a decrease in number, cannot, of necessity, apply to an acid 

 curve such as is characteristic for the streptococcus. The work 

 of CuUen and Chesney (1918) on pneumococci has shown a close 

 relationship between growth-rate and speed of acid production 

 in plain broth, and accordingly these observers have concluded 

 that acid formation is to be considered as an active metabohc 

 process, closely associated with the growth activities of the 

 organism. In examining the curves of Cullen and Chesney one 

 is struck by the close paralleHsm that exists between the various 

 phases in the life of the pneumococcus, as measured by numbers 

 of viable cells on the one hand, and by acid formation on the 

 other hand. As might be expected, a rise in the growth curve 

 always preceded shghtly a rise in acidity. Lord and Nye (1919) 

 have reported results of similar nature on pneumococci grown 

 in glucose broth. During the first 12 hours of their experiment 

 the medium was found to change in reaction from Ph 7.65 to 

 5.25. Up to this point, a rapid increase in the number of cells 

 was evident, but during the subsequent acidification to the final 

 Ph, 5.15, a rapid decrease in viable organisms was apparent. 



