148 MICROBIOLOGY 



living organisms (organized ferments), or by chemical sub- 

 stances thrown off from the bacteria (unorganized or chemi- 

 cal ferments or enzymes). In the first the action is due to 

 the life processes necessary for the growth of the organisms 

 producing the ferment, as in the formation of acetic acid from 

 alcohol by the action of the vinegar plant, and in the second 

 the enzyme, either within or outside of the organism and hav- 

 ing no direct connection with the growth of the organism, 

 causes a structural change without losing its identity, as in 

 digestion. E. Buchner l Las shown that even in those cases 

 of fermentation in which formerly it was believed the organ- 

 ized cell itself was necessarily concerned, the cell protoplasm 

 squeezed from its capsule is able to cause the same changes 

 .as the organized cells. This brings fermentation by unor- 

 ganized and organized ferments very closely together, the one 

 "being a substance thrown off by the cell, the other a sub- 

 stance ordinarily retained in the cell. The increase of both 

 ceases with the death of the bacteria producing them. These 

 enzymes, even when present in the most minute quantities, 

 liave the power of splitting up or decomposing complex or- 

 ganic compounds into simpler, more easily soluble and dif- 

 fusible molecules. The changes thus made may greatly aid 

 in rendering the foodstuff suitable for bacterial growth. We 

 can only speak of chemical ferments when it can be demon- 

 strated that the fermentation continues in the absence of all 

 living bacteria. This may be accomplished by the addition of 

 disinfectants, carbolic acid, chloroform, ether, etc., to the 

 cultures or by filtration." 



Properties of ferments. Ferments are non-dialyzable. 

 They withstand moderate dry heat, but are usually destroyed 

 in aqueous solutions at a temperature over 70 C. They are 

 injured by acids, especially the inorganic ones, but are re- 

 sistant to all alkalies. A simple example of bacterial fermen- 

 tation of carbohydrates produced by an enzyme is that of 

 grape sugar: 



1 Buchner. Berichte d. Deutsch. chem. Gesellsch., Bd. XXX, 

 117-124 and 1110-1113. 



