382 JAMES M. SHERMAN 



as that made with the calcium salt, and in one very important 

 respect to be superior. 



In the preparation of the calcium lactate broth no attention, 

 so far as the published papers indicate, has been paid to its reac- 

 tion; and considering the reactions of the individual ingredients 

 employed there would seem offhand to be little need for concern 

 about this point. It was noted, however, when broth was tested 

 for its hydrogen-ion concentration, by means of the colorimetric 

 method of Clark and Lubs, (1917) that a value of about pH = 

 5.2 was always obtained. This result (from pH = 5.1 to pH = 

 5.3) was found with Witte pepton as well as with a variety of 

 American brands. 



An inquiry was therefore made into the reactions of the indi- 

 vidual components and of combinations of the several components. 

 Calcium lactate broth was made and at the same time solutions 

 of the various ingredients were prepared separately in the same 

 concentrations as they occur in the broth. These were all steri- 

 lized in the autoclave for twenty minutes at 15 pounds pressure. 

 After cooling, the following results were obtained : 



pH 



2.0 per cent pepton 6.8 



0.5 per cent sodium chloride 7.3 



0.2 per cent dipotassium phosphate 8.2 



2.0 per cent calcium lactate 7.3 



Von Freudenrich and Orla-Jensen broth 5.2 



As is shown by these data, the reaction of the finished broth is 

 much more acid than is anj'^ one of its several components. An- 

 other lot of broth made with the same ingredients, with the excep- 

 tion that sodium lactate was substituted for the calcium salt, gave 

 a reaction of pH = 7.2. 



It would appear then that the explanation is to be found in 

 the reaction between the phosphate and the calcium lactate; and 

 such it seems is the case, as is indicated by the result given below. 

 These solutions were sterilized as were those reported above. 



0.2 per cent dipotassium phosphate 8.2 



2.0 per cent calcium lactate 7.3 



0.2 per cent dipotassium phosphate + 2 per cent calcium lactate. . 4.8 



