EXPERIMENT STATION BULLETINS. 



447 



TABLE XXX. 

 The Hourly Fermenting Capacity of the Stock Lactic as Influenced by Different Stimulants. 



From the above table, it may be concluded that the fermenting ca- 

 pacity of Ihe Stock lactic is about doubled by the use of 5 cc. or 25 cc. 

 of unheated or heated pepsin or rennet filtrate. This does not appear 

 when the yeast is used nor is the action similar in the presence of the 

 filtrate. This last stimulant seems to have an action peculiar to itself. 

 It will be notad that there is a gradual increase in the fermenting ca- 

 pacity as a greater amount of filtrate is added ; this is true in both the 

 heated and in the unheated filtrate, and it will also be noted that the 

 unheated filtrate possesses more stimulating power than the heated as 

 the inoculum is increased. Whether this would be duplicated in a 

 second experiment cannot be stated. 



SUMMARY AND CONCLUSIONS. 



1. Certain acid-reducing yeasts have the property of retaining the 

 vitality and activity of lactic bacteria over a period of a year or more 

 when grown with them in mixed culture in milk or in whey. In the 

 case of the red yeast, the acid-reducing property does not appear to be 

 its chief function. 



2. It is possible that a weak lactic be ''rejnvenated," i. e., have its 

 vitality increased by continued association in mixed culture with the 

 veast LZ, an acid-reducer. 



3. This rejuvenating property of the yeasts is due in part to the acid- 

 reducing function, in the case of yeast LZ partially also to rennet and 

 pepsin-like enzymes produced by the yeast. 



4. One of these enzymes at least is extracellular in old cultures; 

 the rennet-like enzyme and probably the pepsin-like enzyme were 

 separated from yeast LZ by filtration. 



5. Although it was difficult to determine the presence of the pepsin- 

 like enzyme in the filtrate by means of its visible action on the milk, 

 the stimulating action of the filtrate is directly comparable with that 

 of the pure pepsin solution. 



6. The pepsin-like enzyme is the one which stimulates the curding 

 function of the lactic bacteria although at first it was suspected that 

 the lactic organisms in some way caused the rennin in the filtrate to 

 act more quicklv. This seems to be proved conclusivelv by the results 

 in Table XXVlil. 



7. The question was raised as to whether the enzymes acted upon the 

 milk constituents and thus indirectly upon the lactic bacteria, or 

 whether the influence was immediately upon the lactic bacteria. It 



