BACTERIA AND FERMENTATION ll'J 



volume of alcohol in ordinary beer wort. Each of these 

 will be referred to as they occur in considering the five im- 

 portant fermentations already mentioned. 



The general microscopic appearance of yeast cells may be 

 shortly stated as follows : they are round or oval cells, and 

 , by budding become daughter yeasts. Each consists of a 

 membrane and clear homogeneous contents. As they per- 

 form their function of fermentation, vacuoles, fat-globules, 



80 



cOOO 



8 



oo o <x:^ x^ 



Saccharomyces Cerevisi^ 



and other granules make their appearance in the enclosed 

 plasma. As in many vegetable cells a nucleus was detected 

 by Schmitz by means of special methods of staining, Han- 

 sen has found the nucleus in old yeast cells from ** films *' 

 without any special staining. 



I. Alcoholic Fermentation. 



Cause, yeast ; medium, sugar solutions ; result, alcohol and carbonic acid. 



It was Caignard-Latour who first demonstrated that yeast 

 ■cells, by their growth and multiplication, set up a chemical 

 ■change in sugar solutions which resulted in the transference 

 of the oxygen from the hydrogen in the sugar compound to 

 the carbon atoms, that is to say, in the evolution of carbonic 

 acid gas and the production, as a result, of alcohol. If we 

 were to express this in a chemical formula, it would read as 

 follows : 



