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CHAPTER II. 



RESEARCHES ON YEASTS. 



i. CHARACTERISTICS OF THE SACCHAROMYCETES. 



THE method of pure yeast culture described in the last 

 chapter is founded upon the view that the Saccharomycetes 

 occur as definite species, and that the characters which I 

 discovered are suitable for distinguishing them. Should these 

 organisms readily change, one into the other, and the 

 boundary lines thus disappear, as some investigators are 

 inclined to assume, my investigations would, as regards their 

 application to practice, lose most of their significance. This 

 was, therefore, the point upon which my opponents based 

 one of their strongest attacks. The following account deals 

 mainly with brewery yeasts, but in order to make it intelli- 

 gible, I have had to include also some sort of survey of my 

 most important yeast studies. 



It is evident that a systematic examination of the yeasts 

 must be of an experimental nature, and that it must start 

 with endospore formation ; thus it was from this point of view 

 that I commenced my studies in this field. These not only 

 proved that there are different species of the Saccharomycetes , 

 but they also gave the first distinguishing characters for them. 

 It was found, namely, that the temperature curves for the 

 development of spores have in the main the same form, 

 but that the cardinal points, especially those representing 



