142 BACTERIA. 



the presence of a full supply of oxygen, protoplasm under 

 certain conditions cannot bring about complete oxidation, 

 and as a result some of the intermediary products of fer- 

 mentation and decomposition may be formed. 



It is evident, then, that all ferments may be classed under 

 two great heads : firstly, the organized ferments or the active 

 unstable protoplasmic cells of yeasts, bacteria, of plants and 

 animals. Secondly, the unorganized ferments or enzymes 

 which we have spoken of as the separable functions of more 

 highly developed cells, both of them being, however, as- 

 sociated with the nutritive and other metabolic changes of 

 protoplasm, be this protoplasm that of simple vegetable cells 

 or of highly organized gland cells. Hoppe-Seyler classifies 

 the whole of the fermentations as follows : I. ferments which 

 bring about hydration or cause hydrolysis, these being divided 

 into (a) those that act like boiling mineral acids, all of which 

 belong to the enzyme group ; and (b) ferments acting like 

 caustic alkalies in which we have the process of decomposition 

 (i) of fats into glycerine and fatty acids as in saponification, 

 which results from the action both of the organisms directly 

 and of the unorganized ferments, (2) decomposition of amido 

 or ammonia-nitrogen compounds which is also usually 

 associated with hydrolysis. II. In the second group, Hoppe- 

 Seyler places fermentations in which there is transference 

 of oxygen from the hydrogen to the carbon atoms. As 

 examples of this we have (a) lactic acid fermentation in 

 which there is decomposition of certain carbohydrates into 

 lactic acid ; this, as we have seen, being always associated with 

 the presence and activity of a certain group of micro- 

 organisms, (3) the alcoholic fermentation brought about in a 

 similar manner by yeasts, (c) putrefactive decomposition 

 changes, (i) of simple inorganic compounds such as combi- 

 nations of the fatty acids with lime, or (2) of organic com- 

 pounds such as fibrin and other proteids. Then we have 

 also the acetic fermentation already referred to, nitrification 

 or mineralization, chromogenic fermentation and that series 

 of changes in which we have the production of ptomaines. 



Such a classification is specially important when we come 

 to consider the relation of the ordinary fermentation pro- 

 cesses to those that are set up during the course of disease in 

 animals and in plants. 



