HYDEOGEN-ION CONCENTRATION OF BROTH MEDIA 



155 



and further that the degree of variation upon standing was usu- 

 ally as great as upon autoclaving. In view of those findings the 

 possibility of an absorption of sufficient CO2 from the atmosphere 

 to account for the changes noted was considered. Experiments 

 II and III were carried out to decide this point. 



TABLE 5 



Experiment I. Changes in reaction upon autoclaving and standing. (Beef extract 



broth) 



Composition: 



Distilled water 1000 cc. 



Liebig's beef extract 3 grams 



Peptone (Parke, Davis & Co.) 10 grams 



NaCl 5 grams 



* Precipitate. 



Experiment II. 



The effect of exposure in an atmosphere of CO2 

 upon the reaction of broth 



Beef infusion broth, prepared and adjusted as outlined in the 

 preceding experiment, was tubed, autoclaved, and treated as 

 follows: (1) Control-beginning. (2) Exposed twenty-four hours 

 in plugged tubes to an atmosphere of CO2. (3) Control after 

 twenty-four hours. 



The results shown in table 6 indicate that direct exposure of 

 broth to CO2 causes very decided increases in acidity, the amount 

 of increase becoming greater as the alkalinity of the broth 



