EXPERIMENT STATION BULLETINS. 



439 



From these results it may be assumed that the acid-producing func- 

 tion and possibly the fermenting power of the lactic organism is stimu- 

 lated by the presence of an enzyme in the filtrate. This may or may 

 not be the same enzyme which causes the curding of the milk. 



Expt. V. 



The Influence of the Addition of Varying Amounts of a Milk Culture 

 of the Yeast LZ to Cultures of the Stock Lactic. 



This experiment was carried on for the purpose of comparing the 

 effect of a milk culture of LZ upon the Stock lactic with that of the 

 filtrate of the yeast (Expt. Ill, Table XX). 



A 17 day milk culture of the Stock lactic and a month old culture 

 of LZ were used. To each of 4 flasks containing 250 cc. sterile milk, 

 0.1 cc. of the Stock lactic culture was added; to 3 of these was added 

 respectively 1 cc, 5 cc. and 25 cc. of the yeast culture. The milk w'as 

 well shaken up in each case and plated immediately. The plates were 

 kept at 37°C. for 48 hours to prevent the growth of the yeast on the 

 plates and thus allow the lactic bacteria to be counted in pure culture 

 Plates and titrations were made as in Expt. III. 



TABLE XXII. 

 Stimulation of Functions oj the Stock Lactic as Influenced by Varying Amounts c/ a Pure Culture cf the Yeast LZ as Inoculum 



*Abnormally higli counts due to contaminating organisms, 

 ing capacity number. 



**Fermenting capacity at 3 days. 

 [ ***Fermenting capacity at 2 days. 



These were not taken into account in determining the ferment- 



The results in Table XXII show that a very marked difference occurs 

 when greater or lesser quantities of the yeast culture are added to the 

 milk culture of Stock lactic, especially in comparison with the pure 

 culture of the Stock lactic. In the pure culture the count per cc, also 

 the acidity gradually increases while in the lactic culture plus the 

 yeast, the greater the quantity of yeast inoculum, the more rapidly does 

 the acidity and the bacterial count rise and the sooner the number of 

 bacteria per cc decreases. From the time that the milk cultures were 

 inoculated until the maximum bacterial count was reached the ratio of 

 multiplication runs as follows: Stock lactic : Stock lactic + 1 cc. 

 yeast culture : Stock lactic + 5 cc. yeast culture : Stock lactic -|- 25 

 cc. yeast culture = 0.3 : 1 : 2 : 4. This ratio of multiplication was 



