180 LAURENCE F. FOSTER 



sources of inocula. H. Jones (1920) has recently observed that 

 in the case of pathogenic streptococci the age of the parent 

 culture employed may exert a considerable influence upon the 

 abundance of growth in sub-cultures which may, in turn, be 

 reflected in the final Ph values. He also observed that cultures 

 which were placed under conditions which tended to delay growth 

 failed to show the characteristic final Ph. The statement fre- 

 quently made that the final Ph of an organism is eventually 

 reached, provided the culture exhibits growth, obviously can not 

 apply to a dehcate organism such as the streptococcus. Thro 

 (1915) called attention to the same fact in his observation that 

 with streptococci variations in luxuriance of growth were asso- 

 ciated with differences in the quantities of acid substances 

 produced. 



Slator (1916) has devised an ingenious method for measuring 

 the rate of growth of a lactic acid-forming organism through an 

 indirect application of the titration values obtained at definite 

 intervals throughout the course of the experiment. Using the 

 formula suggested in a previous work (1917) he was able to show 

 close agreement in the values of the constant, k, in different 

 determinations. The possibility of simultaneous acid and alka- 

 line fermentations in cultures of certain organisms has been 

 emphasized by Ayers and Rupp (1918) who state that such 

 actions may complicate and decrease the value of acidity deter- 

 minations in certain cases. Methods of measuring both fermen- 

 tations have been suggested by these investigators. 



From the foregoing review it would appear that a study of the 

 progress of reaction changes in cultures of Streptococcus hemolyt- 

 icus, in order to furnish data of value, must of necessity entail 

 an investigation of a number of interacting factors. Accord- 

 ingly, experiments were planned to study the rate of acid 

 formation as influenced by the following: (1) Amount of inocu- 

 lum; (2) age of parent culture; (3) presence of a body fluid, horse 

 serum, (4) initial reaction of medium. 



