554 RESPIRATION AND FERMENTATION 



butylicns as the result of prolonged cultivation at a high temperature, or 

 owing to the presence of an abundance of oxygen. Grimbert a has shown 

 that Bacillus ortliobntylicns, after previous cultivation on dextrose, ferments 

 inulin with a copious production of butyl-alcohol, and there is other evidence 

 to show that the power of exciting fermentation may undergo more or less 

 marked modification. 



It is possible that in certain cases the fermentative activity is simply 

 the result of an increase in the essential respiratory katabolism (Sect. 102), or 

 is due to special processes which accompany and run parallel with the latter. 

 It has already been mentioned that during the aerobic existence of yeast 

 the fermentation of alcohol may no longer be essential, or may cease to 

 be of use in respiratory metabolism although it still persists. Hence in 

 such cases it may be possible to distinguish clearly between accidental 

 processes of fermentation and those which form an essential feature of 

 respiratory metabolism. During aerobic existence the greatest amount of 

 energy is obtained by complete combustion into carbon dioxide and water, 

 but it often happens that the regulatory production of acids becomes 

 of great importance (Sect. 85), and indeed the accumulation of acids, 

 alcohol, &c. may be of great use in the competition with other organisms 

 provided that the plant is relatively resistant to the injurious effect exer- 

 cised by its own products. From a general economic point of view the 

 partial decompositions induced by anaerobes, as well as by certain aerobes, 

 are of the highest importance, and many lower organisms work quite as 

 economically as do certain fungi, although the latter induce the complete 

 combustion of enormous masses of organic material (Sect. 95), and would 

 certainly be termed ferment-organisms if other products than volatile 

 carbon dioxide and water resulted from their intense disintegratory activity. 

 In every plant only a certain portion, and often a very small fraction, of 

 the food is used for plastic and formative purposes (Sects. 50 and 77), and 

 in alcoholic and lactic fermentations 95 per cent, of the sugar supplied may 

 be fermented, and only 5 per cent, permanently assimilated. 



A production of secretory and excretory products is a constant 

 accompaniment of all metabolism, and since the extent to which the 

 respiratory materials undergo total combustion varies within wide limits, 

 it is evident that no sharp line of demarcation can be drawn between 

 fermentation and respiration. Thus according to circumstances Aspergillus 

 may produce much or little oxalic acid from sugar, Mucor racemosus much 

 alcohol or none at all according as oxygen is absent or present. It is, 

 however, permissible to use the popular term fermentation to include all 



Abth. ii, Bd. in, p. 102), certain varieties of Aspergillus niger have not the power of exciting oxalic 

 fermentation. 



1 Ann. d. 1'Inst. Pasteur, 1893, T. vir, p. 401. 



