EXPERIMENT STATION BULLETINS. 433 



Summarizing the above scores, Strain 2 gave a sharp clean acid 

 throughout all the cultures, Strain 4 was mildly acid and both Bact. 

 hiilgaricum and No. 53B2 })roduoed a very high acid except in the 

 younger cultures. Off-flavors in all cases were found to be due to the 

 specific yeast which had been picked up in the effort to isolate pure 

 cultures from thickly populated plates. 



It was noted that the pure cultures of high acid lactic bacteria 

 isolated from their combined cultures with the different yeasts in milk, 

 produced acid faster than the same bacteria from the duplicate cultures 

 in whey. Bact. hulgaricum from the mixed culture of Bact. hulfjaricum 

 with the yeast DG in whey is the exception to this. (See Table XV.) 

 This seems to show that the stimulation produced by the constituents of 

 milk not common to whey is still in effect after the removal of the lactic 

 bacteria from their direct influence. 



PART II. 



INFLUENCE OP ENZYMES PRODUCED BY YEAST LZ. 



The influence that the yeast LZ has upon the different lactic bacteria 

 w«s attributed to some enzyme or enzymes produced by the yeast. To 

 ascertain whether this influence was exerted by extracellular substances, 

 a yv^hej culture of the red yeast was filtered through a bacteria imper- 

 vious filter and the action of the filtrate compared with that of the cul- 

 ture itself. 



Expt. I. 



Determination of Extracellular Substances in the Filtrate of Yeast LZ. 



A 4 months' old whey culture of LZ was filtered through a Kitasato 

 pencil filter, obtaining about 50 cc. of filtrate. A flask containing 250 cc. 

 of sterile milk was inoculated with 1 cc. of this filtrate pnd 1 cc. of a 

 3 weeks old milk culture of Lactone and another flask of sterile milk 

 inoculated with 1 cc. of Lactone for a check. Both flasks and the fil- 

 trate were plated immediately. 



As soon as the milk containing the filtrate curded, plates were again 

 made and the acidity recorded from each flask; titrations and platings 

 were made from time to time for over a month. The results are 

 recorded in Table XVI. 



The fermenting capacity of the lactic bacteria in this experiment and 

 in those following is calculated according to Dr. Rahn's formula (1) 



X = . ,,,^ ^°f ^ , , "a" being the initial number of bacteria, "b" being the 



t (b - a) log* ' o 7 o 



largest number of cells, "t" the time at which ''b" was determined, and 

 "S" the increase in the acidity of the medium, "x" is the number of 

 milligrams of ferment lactic acid produced per hour by a single cell. 

 These calculations were made in the hopes that some additional light 

 would be thrown upon the action of an aggregation of cells of lactic 

 organisms. 

 55 



