HYDROGEN-ION CONCENTRATION OF BROTH MEDIA 



153 



the three different temperatures the same general tendencies as 

 have been observed in series IV may be noted. 



It appears that there is no marked consistency in the variations 

 which a given type of broth medium may exhibit as a result of 

 autoclaving and standing. The same conclusions have been 

 reached by Grace and Highberger (1920b) working with beef ex- 

 tract broth. Itano (1916a) however, reported only decreases in 

 acidity in lots of extract broth adjusted throughout a wide range 



TABLE 3 



Experiment I. Changes in reaction upon autoclaving and standing. (Bacto-beef 



broth) 



Composition: 



Distilled water 1000 cc. 



Bacto-beef 50 grams 



Peptone (Parke, Davis & Co.) 10 grams 



NaCl 5 grams 



* Precipitate. 



of Ph. His medium contained 2 per cent peptone which, as is 

 well known, acts as a strong buffer. By steriUzing the compo- 

 nents separately he was able to avoid anything more than shght 

 alterations in reaction. No data were collected relative to the 

 possibility of changes upon standing. The discrepancies appear- 

 ing in the present beef infusion series were not so unexpected 

 when it is considered that two different lots of beef were employed 

 in their preparation, but the lack of uniformity in the changes 



