ALCOHOLIC FERMENTATION OF SUGAR BY YEAST. 589 



energetic fermentation. Two species, beer and wine 

 yeast, act most powerfully. The former is constantly 

 cultivated in beer wort ; fresh fermentation is set up by 

 the addition of the yeast from fermenting wort to fresh 

 fermentescible fluid. According to the more or less 

 violent progress of the fermentation, high or low yeast 

 is obtained; in the former the budding takes place more 

 rapidly, and we thus obtain groups of cells which are 

 readily taken up by the stream of carbonic acid and 

 carried to the surface. The wine yeast S. ellipsoideus 

 is the form which is most widely distributed in 

 nature ; it establishes itself spontaneously in the most 

 various saccharine solutions when exposed to the 

 entrance of air, or it is introduced into these, for ex- 

 ample, by the skins of the grapes, on which it is con- 

 stantly found. The other forms of yeast, S. apiculatus, 

 exiguus, &c., appear to possess a less degree of vegeta- 

 tive energy and fermentative action. In the case of 

 some, as, for example, pink yeast (rosa hefe), no fermen- 

 tative action has, as yet, been noted ; mycoderma only 

 excites a temporary and trivial fermentation when it is 

 artificially compelled to grow at the bottom of fluids. 



The yeast-like growths of some of the mould fungi Fermentative 

 have a more powerful fermentative action than the forms mould and 

 of yeast last mentioned, in that, when immersed in sugar fission 

 solution, they set up a fairly energetic decomposition of 

 the sugar, with the formation of alcohol and carbonic 

 acid ; at the same time they approach true yeast in 

 their conditions as regards form and growth. These 

 properties are most marked in Mucor racemosus, M. 

 cercinelloides, M. spinosus ; they are less developed in 

 Mucor mucedo, and hardly at all in Mucor stolonifer. 

 Other mould fungi are also able to produce traces of 

 alcohol and carbonic acid when they grow in saccharine 

 solutions in the absence of oxygen ; but the amount 

 produced cannot be at all compared with that formed by 

 the species of mucor and by the true yeasts, and only 

 depends on the intramolecular respiration, by means of 

 which also the cells of any of the higher plants can 

 form alcohol and carbonic acid. Further, in the fer- 



