ENSILAGE AND FERMENTATION. 225 



an accumulation of experimental evidence that could not be contro- 

 verted. He proved that sugar was acted upon by a variety of fer- 

 ments, each giving its own peculiar product, and that the different 

 kinds of fermentation, properly so called, as the alcoholic, the lactic, 

 the acetic, the viscous, the butyric, and putrefactive, were each the 

 result of the vital activity of distinct and specific organisms. 



Ferments are now generally divided into two classes : 1. The so- 

 called soluble or chemical ferments, as acids and diastase, which 

 " invert " cane-sugar and transform it into dextrose, or change starch 

 into dextrin. These soluble ferments, according to Dumas, " always 

 sacrifice themselves in the exercise of their activity," but they do not 

 produce fermentation in the strict sense of the term. 2. The true 

 ferments, which, through the investigations of Pasteur, are now known 

 to be living organisms that produce fermentation as a function of 

 their vital activity. Unlike the soluble ferments, these living organ- 

 isms increase at the expense of the substances fermented. The true 

 fermentations are therefore purely physiological processes, which are 

 defined by Pasteur as "the direct consequence of the processes of 

 nutrition, assimilation, and life, when they are carried on without the 

 agency of free oxygen," or, " as a result of life without air." 



The organized ferments, which belong to the class of fungi, may 

 be divided into two groups, the saccharomycetes, or budding fungi — 

 the active agents of alcoholic fermentation, of which yeast may be 

 taken as the type — and the schizomycetes, or fission fungi, which in- 

 clude the lactic, the butyric, and similar ferments, and the organisms 

 that produce putrefaction ; most of them are of the form known as 

 bacteria, and they multiply rapidly by subdivision. It is probable 

 that all the members of both groups propagate by means of spores, as 

 well as by their special processes of budding and fission, but there 

 are many species in which reproduction by spores has not been ob- 

 served. The living organisms (bacteria) found in samples of fresh 

 ensilage belong to the group of schizomycetes. Thus far no members 

 of the group of saccharomycetes (yeast or alcoholic ferments) have 

 been observed, by me, in sarnples from the interior of the silo that 

 had not been exposed to the air. When a large surface of ensilage is 

 exposed to the air, after the silo is opened, a variety of ferments may 

 make their appearance, and with them several species of molds, but 

 they are evidently produced from germs derived from the air. 



The mold-fungi are not included in the class of ferments, as Pasteur 

 has proved that they act as ferments under exceptional conditions only, 

 and even then they do not produce active fermentation. The alco- 

 holic ferments have been studied more thoroughly than the others, 

 from their importance in the manufacture of beer, wine, etc., but many 

 of the facts developed in their investigation are undoubtedly appli- 

 cable to other ferments: 



From Pasteur's experiments with fruits in an atmosphere of car- 



VOL. XXV. — 15 



