EXPERIMENT STATION BULLETINS. 449 



pared with the original pure culture and no change had been effected. 



16. It is noteworthy that the mixed cultures which have become con- 

 taminated with molds or other bacteria and yeasts have not lost their 

 power of retaining the vitality of the lactics except in one instance. 

 Foreign organisms seem to have no appreciable effect on the lactic 

 bacterium and the yeast after the symbiosis of the latter had once been 

 established. 



17. In the case of the mixed culture of the yeast LZ with different 

 lactic bacteria, the lactic bacterium, even a very weak organism, has a 

 chance to produce its maximum amount of acid before any appreciable 

 acid destruction can take place. 



IS. The high-acid-producing organism. No. 53B2, unlike liact. hul- 

 garicum and ordinary lactic bacteria, survives a long sojourn at its 

 maximum acidity (in the neighborhood of +280°). The red yeast grows 

 most difficultly with this lactic organism. 



19. The red yeast LZ produces several enzymes and other substances 

 which when the yeast is growing in combined culture with a lactic bac- 

 terium, stimulate the lactic organisms to greater activity causing the 

 production of a greater number of cells and a larger quantity of acid 

 than would be produced normally in pure culture. This process of 

 stimulation if continued over a period of several months causes a weak 

 lactic to increase its activity until it becomes a typical lactic organism 

 in regard to its power of producing acid, causing litmus reduction and 

 curding milk. The required time for rejuvenating naturally varies with 

 the individuality of the culture, sometimes 3 weeks, sometimes 3 months 

 or longer of symbiotic relationship being necessary to effect the muta- 

 tion. 



20. In order that the lactic bacterium obtain the most possible bene- 

 fit from the yeast, the yeast itself must be present in the medium with 

 the lactic organism. The several products of each organism appear to 

 attain an equilibrium which is similar to and comparable with that 

 reached in strictly chemical reactions. This equilibrium is happily 

 destructive neither to the lactic nor to the yeast Avithin the periods noted. 



21. Many of the above statements are corroborative in their kind, of 

 the conclusions drawn in "Bacterial Associations in the Souring of 

 Milk" by Marshall and Farrand, concerning the associative action of 

 other bacteria with lactic organisms. 



22. This phenomenon of associative action in time may solve the 

 problem of keeping other short-lived organisms almost indefinitely with- 

 out frequent transfers. 



Further studies are being undertaken dealing with other phases of this 

 interesting problem. 



BIBLIOGRAPHY. 



1. Rahn, O., "The Fermenting Capacity of the Average Single Cell of 



Bacterium Lactis Acidi." Tech. Bui, 10, Mich. Agr. Expt. Sta. 



2. Marshall, Charles E., and Farrand, Bell, "Bacterial Associations in 



the Souring of Milk." Spec. Bui. No. 42, 1908, Mich. Agr. Expt. 

 Sta. 



3. Lafar, "ITandbuch d. Tech. Mykologie". Bd. IV, S 282-299. 



57 



