PART V. 



THE BLASTOMYCETES, OR YEAST FUNGI 



The yeast fungi are divided into two groups : 



() Saccharomycetes or true yeasts, in which true spore formation 

 occurs. 



(6) Torulse, in which no spore formation has been observed. 



The Blastomycetes reproduce themselves by gemmation or budding, 

 which distinguishes them from the schizomycetes or bacteria, which 

 reproduce themselves by fission or simple division. From the hypho- 

 mycetes or mould fungi the blastomycetes are distinguished by being 

 unicellular and by asexual reproduction. 



The yeasts employed for commercial purposes consist of a mixture of 

 different species. We are indebted to the researches and experiments 

 of Hansen for our present knowledge of the various changes produced 

 by the different species during fermentation, as well as for the method 

 of isolating them by means of plate cultures instituted with acid or 

 beer-wort gelatine. Observation of the following conditions enables the 

 various species to be differentiated during development. 



1 . The temperature at which ascospores develop. 



2. The characters of the film or zoogloea mass of cells forming on 

 the surface of the fluid during fermentation. 



3. The changes produced in the various kinds of sugar. 



4. Whether the variety under observation causes a top or bottom 

 fermentation. 



A surface or top fermentation yeast grows and forms spores readily 

 at 14 to 18 C. ; while a bottom fermentation yeast grows at 4 to 

 10 C. in the bottom of the fluid, and forms spores only with difficulty. 



METHOD OF OBTAINING PURE CULTURES ON A 

 SMALL SCALE. 



1. A Pasteur flask containing the wort to be experimented with is 

 started and carried on as vigorously as possible. 



