FERMENTATION. 14! 



point of very considerable interest, for we find that under 

 certain conditions there comes to be a contest between the 

 animal cells and the lower vegetable cells. As Wood well 

 puts it, " the reaction of the cells upon each other may turn 

 on the sum of the conditions of existence to which they are 

 exposed happening to favour one more than the other, thus 

 when two organisms are sown together in a culture fluid, 

 which will overgrow the other may depend upon the relative 

 quantity of the two primarily introduced, the nature and 

 reaction of the media, and the temperature at which they 

 are held." Fermentation, then, is due to the action of highly 

 specialized cells. That this is so is indicated by the usual 

 presence of enzymes and also by the fact that they exert this 

 specific action in their highest degree only under a certain 

 set of specific conditions which vary in the case of each 

 organism. Each organism has become adapted to a 

 certain medium, and is so specialized as to have the power of 

 splitting it up under certain conditions in a specific way. 

 This is also indicated by the fact that as the conditions 

 become unfavourable, less and less of the specific product 

 (relatively to the bye products) is produced. Although we 

 shall have more to say in connection with the subject of the 

 specific infectivity of micro-organisms in disease, it may here 

 be pointed out that fermentation is due, in great part, to the 

 action of cells which have the power of developing a special 

 enzyme function ; that these cells are usually more highly 

 specialized during the stages when they bring about their 

 specific action ; that this is associated to a certain extent with 

 diminished activity of the protoplasm directly on the sub- 

 stances to be fermented ; that most processes where there is 

 the formation of an enzyme, or a special poison, take place 

 most actively when there is a complete or partial cutting off 

 of the supply of oxygen ; that the cells in this condition 

 usually develop a more or less perfect cell membrane which 

 characterizes the formation of zoogloea masses ; that this in- 

 complete oxidation also characterizes the formation of 

 toxines ; that the same rules hold good in the formation of 

 most of the products of the lower vegetable organisms 

 and of the individual cells of animal tissues with complete 

 oxidation and the formation of carbonic acid gas and 

 water ; that when incomplete oxidation takes place various 

 specific products make their appearance ; but that even in 



