HYDEOGEN-ION CONCENTRATION OF BROTH MEDIA 147 



bring the material to an initial Ph of 8.6. Davis also emphasizes 

 the superiority of the autoclave over the Arnold for media steril- 

 ization pointing out that prolonged heating is always to be avoided 

 in order that the vitamine or hormone content may not undergo 

 destruction. On the other hand, Fennel and Fisher (1919) report 

 that in the preparation of over one hundred lots of beef infusion 

 broth the initial Ph of 7.8 did not show variation as a result of 

 autoclaving. In connection with his study of the effect of initial 

 reaction of a medium upon Corynehacterium diphtheriae, Bunker 

 (1919) noted certain reaction changes in his media upon steriliza- 

 tion. The variations appeared almost entirely on the alkaline 

 side and were always noted as increases in acidity. ^ Very re- 

 cently, Grace and Highberger (1920b) have carried out experi- 

 ments with extract broth which seem to indicate that changes in 

 reaction upon sterilization may not be of any greater order than 

 are the changes which a medium may undergo simply upon stand- 

 ing, following autoclaving. The variations of greatest magnitude 

 occurred in the alkaline range and all changes were toward a 

 more acid reaction. No consistent tendencies could be detected, 

 therefore it was not possible to come to definite conclusions as 

 to the reasons for the observed changes. However, the possibili- 

 ties of the influence of glass and atmospheric CO2, as well as of 

 slow hydrolysis, were suggested. 



Early in the present investigation it was noted that culture 

 media (broth) adjusted to definite Ph levels underwent changes 

 in reaction upon autoclaving, thus rendering difficult the prepara- 

 tion of broth of desked reaction. Consequently it was consid- 

 ered important to investigate these changes with a hope of finding 

 an explanation and perhaps of discovering some means of avoid- 

 ing them. 



METHODS AND TECHNIC 



Standard solutions 



All solutions were prepared according to the methods outlined 

 by Clark and Lubs (1916a, 1917a) from boric acid and salts which 



^ The term acidity in the present paper signifies true acidity as expressed in 

 terms of Ph. 



