624 VITAL ACTIONS OF THE LOWER FUNGI. 



they assimilate their nutriment, grow and multiply, 

 break up the nutriment in their protoplasm, and taking 

 up oxygen form the products of tissue change formerly 

 described. Or oxygen only may be wanting in the 

 medium ; in that case the intramolecular respiration, 

 with its insignificant destructive tissue change, can for 

 some time maintain the life of the organisms. Or, in 

 the third place, a fermentescible material, suitable for 

 the organism in question, is present ; in that case 

 extensive decomposition of the material occurs, along 

 with active multiplication of the organisms ; this takes 

 place as regards the majority of organisms in every case 

 where the other conditions of life are favourable, in the 

 case of some (bacillus butyricus) it only occurs so long 

 as oxygen is at the same time absent. 



The fermenta- The splitting up of the material, as the result of 

 tiyp action, fermentation, differs in many respects from the ordinary 

 tissue change. In the fermentation very much larger 

 quantities of material are acted on than are otherwise 

 necessary for the nourishment of the same number of 

 organisms. Further, the decomposition is a relatively 

 incomplete one ; in the respiratory tissue change the 

 nutrient substances are oxidised to simple compounds, 

 but in the fermentation the materials of the nutrient 

 medium remain, for the most part, in the form of com- 

 plex molecules, and it is only some of the more simple 

 groups that are broken up. Finally, in the fermenta- 

 tions the oxygen does not take an important part in the 

 breaking up of the materials, and more especially in 

 their conversion into the end products, as is the case in 

 respiration, but the whole decomposition often takes 

 place without any aid from oxygen, which only acts 

 secondarily and then causes oxidation. 



In correspondence with these differences between the 

 ordinary tissue change and fermentation we have the 

 fact that many chemical materials act as nutriment 

 without being able to act as fermentescible materials, 

 and vice versd ; thus formic acid cannot serve as nutri- 

 ment but is broken up by fermentation, while, on the 

 other hand, the benzole derivatives and the higher fatty 



