134 PHYSIOLOGICAL CHEMISTRY. 



ALCOHOLIC FERMENTATION. 



As mentioned at the outset the phenomena of alcoholic fer- 

 mentation were the first to claim attention and many of the 

 fundamental conditions were empirically established long be- 

 fore the part played by yeast in the process was recognized. 

 After the investigations of Pasteur our knowledge in this field 

 rapidly widened. 



Yeast. The common agent of alcoholic fermentation is 

 known as yeast, but under this term are included a very large 

 number of really distinct species. In fact several different 

 genera may be and actually are employed in practice. The 

 following table gives an idea of the relations of the commoner 

 organisms classed among the alcoholic ferments. The yeasts 

 with many other cells are classed in a group of the budding 

 fungi, or Eumycetes, as distinguished from the fission fungi 

 or Schizomycetes. 



Family Saccharomycetes 



Genus Monospora Saccharomyces Schizosaccharomyces 



r Cerevisise 



Species -\ Ellipsoideus 



I Pastorianus 

 and others. 



A few molds, also, bring about alcoholic fermentation. We 

 have included here Mucor niucedo, Mucor racemosus, Mucor 

 Rouxii and others which are not in any way technically 

 useful. 



Ordinarily, however, we take as the type of a yeast the 

 common beer yeast Saccharomyces cerevisia, which is a cul- 

 tivated species employed in fermentation by brewers and dis- 

 tillers. In the natural wine fermentation other species seem 

 to be the most active. These are found on the skin of the 

 grape and hence find their way into the juice after crushing. 

 5. apiculatus and S. ellipsoideus are the names of two of the 

 most important of the species active in this way. The com- 



