102 RESEARCHES ON YEASTS. 



already become directly applicable in practice. What has 

 long been achieved in horticulture and agriculture will also be 

 attained in this case, and, in fact, with a more thorough com- 

 prehension of the active factors ; for the one-cell organism is a 

 far more favourable object for such experiments than the 

 more highly-developed flowering plants. 



But even when we have got so far that we can with 

 certainty determine the action of different chemical and 

 physical factors, and are enabled to bring about the changes 

 in the desired direction, we still know nothing as to what 

 it is in the cells which effects the changes or which produces 

 this or that result. These great problems again lead us 

 into new paths of study, and point especially to the investi- 

 gation of the protoplasm as the direction which will some 

 day lead to their solution. Every problem gives rise to a 

 greater and more difficult one, and science is never at a 

 standstill. 



5. MAIN RESULTS. 



Both the theoretical investigations in the laboratory and 

 those of a purely practical nature carried out in the brewery 

 have thus shown that there are different species of Saccharo- 

 myces, and, in fact, not only of the so-called wild yeasts, but also 

 well-characterised high and low yeasts which are employed in 

 breweries. Exposed to different external influences, they 

 may vary to a considerable extent, but in most cases they 

 return to their original condition when they are cultivated for 

 a length of time under normal conditions. New species or 

 varieties can, however, be formed by proper treatment con- 

 tinued for a length of time, whose newly-acquired properties 

 are perpetuated in the different cultures. As long as the yeasts 

 were cultivated tinder the conditions obtaining in the brewery 

 their properties varied but slightly : it thus follows that in 

 practice we can and must regard them as definite species, and 

 ive should adapt our method accordingly. 



