EYES AND FLAVOR IN EMMENTAL CHEESE 383 



The marked acidity of the lactate-phosphate mLxture is prob- 

 ably explained by the formation of acid phosphates and lactic acid 

 along with the insoluble calcium phosphate. 



Aside from the case of this particular broth, the principle here 

 illustrated should be given more general consideration in the 

 formulation of culture media. It would seem, a 'priori, that there 

 is danger of such a shift in the hydrogen-ion concentration upon 

 sterilization of any medium which contains calcium or magnesium 

 and a phosphate, if the calcium-magnesium portion is in excess 

 of the phosphate. This principle is violated in many of the syn- 

 thetic media which are recorded in bacteriological literature. It 

 is obvious also that the buffering effect of the phosphate is lost 

 in such a combination. 



In the recommendation that sodium lactate be used in the place 

 of the calcium salt, it has been assumed that the dibasic phosphate 

 employed in this medium serves some useful purpose. As a mat- 

 ter of fact, in pure culture, the lactate-fermenting bacteria of Swiss 

 cheese grow very well in broth containing only pepton and either 

 calcium or sodium lactate. This does not prove that the simpli- 

 fied medium would be just as good for quantitative estimations in 

 which the seedings are very light. 



In the work here reported quantitative determinations were 

 made in a broth containing 1 per cent pepton, 1 per cent dried 

 yeast and 1 per cent lactic acid (as sodium lactate) . This broth 

 supports a very active growth of the lactate-fermenters and is an 

 excellent one for quantitative purposes. 



Approximate numbers found 



Quantitative dilutions of cheese were planted in broth composed 

 of 1 per cent each of pepton, dried yeast, and lactic acid (in the 

 form of sodium lactate) . Dilutions of from 0.01 to 0.000,001 gram 

 of cheese were tested. After incubation for four weeks at 30°C. 

 the cultures were acidulated and subjected to steam distillation 

 to determine the formation of volatile acids. Control flasks con- 

 taining pepton-yeast broth without the lactate, inoculated with 

 the same dilutions, were run in order to avoid any possible error 

 through the measurement of the relatively small amounts of vola- 



