174 LAURENCE F. FOSTER 



plotted using the cubic centimeter of acid as abscissae and the 

 Ph readings as ordinates. Reference to the curves (fig. 1) will 

 show that horse serum in these concentrations exerts a slight 

 but distinct buffer effect. The 10 per cent series does not show 

 a much greater buffer action than the 5 per cent series however, 

 and the effect in no case is anything like that noted in the case 

 of K2HPO4 (experiment III). 



III. THE RATE OF ACIDITY FORMATION IN CULTURES OF STREPTO- 

 COCCUS HEMOLYTICUS 



Considerable work by a number of investigators has demon- 

 strated that the life cycle of a given organism, as measured by 

 the number of viable cells present at various intervals following 

 inoculation, may be separated into very definite periods. Thus, 

 Chesney (1916) has suggested a division into four phases: (1) 

 latent period or lag, (2) maximum growth period, (3) stationary 

 period, (4) period of decline. 



No sharp dividing lines may be drawn between the periods, 

 and their duration will vary in the case of the same organism 

 with such factors as the amount of inoculum, age of parent 

 culture, and initial reaction of the medium. Buchanan (1918) 

 described seven periods in the life of an organism: (1) initial 

 stationary phase; (2) lag phase when growth proceeds at a slowly 

 accelerating rate; (3) maximum or logarithmic period in which 

 the rate of increase in numbers is constant; (4) period of nega- 

 tive growth acceleration, the organisms are increasing at a 

 decreasing rate; (5) maximum stationary period; no increase in 

 numbers; (6) period of accelerated death, decrease in taking 

 place at an increasing rate; (7) logarithmic death phase; death is 

 occurring at a constant rate. 



With the development of procedures for the mathematical 

 analysis of the several phases (Buchner, Longard, and Riedhn 

 (1887), Buchanan (1918), Slator (1917), Ledingham and Penfold 

 (1914) has come the possibihty of more definite knowledge con- 

 cerning the growth activities of organisms. 



