146 LAURENCE F. FOSTER AND SAMUEL B. RANDALL 



(1916) states that properly prepared media do not increase ap- 

 preciably in acidity when the length of sterilization is increased 

 or when repeated autoclavings are carried out. It is a known 

 fact that many proteins may exist in solution only between cer- 

 tain limits of hydrogen-ion concentration and that slight changes, 

 at or near the critical zones, cause the formation of precipitates. 

 This phenomenon occurs in peptone solutions and as Kligler 



(1917) has shown it is possible to establish the limits of Ph which 

 determine precipitation for each brand of peptone.- Cook and 

 Lefevre (1918) showed that as much as 12 per cent of peptone 

 may be lost through precipitation depending on whether this 

 material were added previous to coagulation and filtration or sub- 

 sequently. That a change in Ph accompanies such a precipitation 

 in media has been found by Clark (1915a) who reported a fall 

 in Ph of 0.80 (from 8.52 to 7.72) in an infusion broth containing 

 0.5 per cent K2HPO4. Itano (1916a) using the hydrogen elec- 

 trode in his Ph measurements, was able to establish a rough cor- 

 relation between the changes in Ph of an extract broth upon auto- 

 claving and the increase in COOIi groups as determined by the 

 formol titration of Sorensen. Strangely enough the changes in Ph 

 reported by Itano were always of the nature of an increase in 

 alkalinity, and with this there appeared an increase in formol- 

 titrating nitrogen, indicating that hydrolysis had occurred. As 

 a result of boiling the broth for forty-five minutes this observer 

 found that the material became stable as regards further changes 

 in Ph. This last experiment, however, was tried only on media 

 adjusted between Ph 5.45 and 6.88. By steriHzing the constitu- 

 ents of his media separately it was possible to adjust to the desired 

 Ph and obtain values which remained fairly constant throughout 

 the entire experiment. Norton (1919) has reported that appreci- 

 able changes in the reaction of neutral and alkaline media, but little 

 variation in the acid range, result from steriUzation. Davis (1920) , 

 in recognition of the possibility of a change in the Ph of media 

 adjusted in the alkaline range, has suggested that for the proper 

 preparation of a glucose broth of Ph 8.0-8.2 reaction it is well to 



2 The symbol Ph of Sorensen is used throughout to designate the hydrogen- 

 ion concentration. 



