448 STATE BOARD OF AGRICULTURE. 



was ascertained that the rennet enz.vme in the filtrate acts in part upon 

 the milk constituents (see Table XXI) but the most marked action of 

 the filtrate is upon the lactic bacterium itself; two principles of the 

 filtrate are concerned in this, one destroyed and the other not destroyed 

 by heat. The former is most likely the pepsin-like enzyme or the com- 

 bined pei)sin and rennin and the latter, certain food principles, ])0ssibly 

 })eptones, produced by the yeast which are not changed by heating. 



8. As commercial rennet is never wholly free from pepsin the re- 

 sults in Table XXYII could not be used to refute the immediately pre- 

 ceding statement. 



9. The influence of the filtrate upon the virility of the lactic bac- 

 terium increases directly as the amount of filtrated inoculum is in- 

 creased; this is true in the heated as well as in the unheated filtrate. 



10. The filtrate both heated and unheated has a marked stimulating 

 effect both uj)on the virility and upon the acid production of weak lactic 

 bacteria. This results in the rapid dying-out of the lactic bacteria in 

 the cultures to which the veast filtrate has been added. This dving-out 

 of the lactic organisms may be due to the exhaustion of vital force fol- 

 lowing the overstimulation caused by the presence of the filtrate. Again, 

 this effect may be attributed to the fact that the organisms have been 

 induced to produce nearly double their usual amount of acid and as 

 a consequence have become hypersusce])tible to their own products. 

 This latter theory is in all i)robability the correct one although the two 

 cannot be distinctly separated. It follows then that a weak lactic bac- 

 terium will live much longer in pure culture in milk if no stimulant is 

 added or if acid formation is prevented. 



11. The hourly fermenting capacities of the weak lactic bacteria as 

 summarized in Tables XXIX and XXX show that the presence of the 

 yeast filtrate, of the pepsin or of the rennin solution causes an increase 

 of the fermenting power to nearly double that of the check. 



12. The yeast used in most of the experiments in this article was the 

 red yeast "LZ" present in the original culture. This was used almost 

 exclusively, for several reasons: the pigment produced renders the pres- 

 ence of this yeast easily discernible to the naked eye; the macroscopic 

 appearance of the mixed cultures of this yeast with lactic bacteria is 

 characteristic; soon after the yeast appears a sj^mmetrical shrinking 

 of the curd occurs, the curd later becomes wholly digested leaving a 

 perfectly clear whey and a plentiful deposit of red yeast cells; this 

 organism does not grow well on ordinary agar and is very susceptible 

 to a temperature very much higher than room temperature; this sensi- 

 tiveness to high temperatures rendered it possible to plate mixed cul- 

 1ures of LZ and a lactic bacterium and obtain counts of the laclic 

 organism alone, simply by placing these plates at 37°C. for 48 hours. 



13. The fact that this red yeast is a strict aerobe and lactic bacteria 

 are facultative, ])referably anaerobes, accounts in all probability for one 

 phase of the beneficial associative action. 



14. It was proved quite conclusively that the acid introduced arti- 

 ficially or produced naturally in milk or whey is destroyed by the yeasts, 

 not merely neutralized. 



15. After sojourning for some time wilh the different yeasts, the 

 several lactic bacteria were isolated and tested to ascertain whether 

 the flavor of the curd had been changed. These cultures were com- 



