The Kinds of Work That Are Done by Plants loi 



into alcohol, and the Yeast plant cannot help it. That is why the 

 Yeast produces the poisonous alcohol, despite the suicidal char- 

 acter of the proceeding. The Yeast, however, can respire in no 

 other way, and with commendable philosophy, prefers a short 

 life, even at the risk of an alcoholic grave, to no life at all. Yet 

 in fact the case is not really so bad, for the alcohol is very volatile, 

 and in Nature commonly evaporates as rapidly as formed; and 

 even when not, the drying up of the liquid and spore-formation 

 allow the yeast to escape and renew its activity at another time 

 and place. If the Yeast plant had nothing to do but respire, 

 the sugar would all be converted to carbon dioxide and alcohol, 

 which are probably the sole products of its respiration. But the 

 Yeast must also make new substance, protoplasm and walls, 

 for which purpose it uses some of the sugar in a different way, 

 along with other substances, and thereby develops incidentally 

 a small percentage of by-products, — glycerin, acids, etc., the pur- 

 suit and capture of which affords a fine joy to the special student 

 of chemistry, especially if some student of biology has previously 

 told him that carbon dioxide and water are the "products of fer- 

 mentation." 



Alcoholic fermentation caused by Yeast is the most typical 

 and familiar kind, but other sorts occur, caused by germs (Bac- 

 teria), or Molds. Thus the souring of milk, the rancification 

 of butter, the genesis of vinegar, and even the development of 

 distinctive flavors in ripening cheese, are products of fermenta- 

 tions, caused in their respiration by various organisms. As these 

 cases illustrate, the secondary products need by no means con- 

 sist only of alcohol, but can include substances of the most diverse 

 chemical natures. All that is requisite is that carbon and oxygen 

 shall be allowed to unite; the matter of the particular compounds 

 is secondary. 



If any doubt could exist that fermentation is simply the respir- 

 ation of the Yeast plant, it would vanish before the remarkable 

 fact that an exactly intermediate step is known between the 



