THEORIES OF FERMENTATION 133 



cells in the last case must have been proportionately more powerful in 

 effecting fermentation. 



All the technical fermentations are, as a matter of fact, anaerobic pro- 

 cesses, for although at first air is contained in the liquids in the vats, and has 

 unhindered access to them, the commencement of the fermentative process 

 alters conditions immediately. The oxygen in the liquid is used up at once 

 by the organisms, and the CO 2 they evolve lies in a heavy stratum over 

 the contents of the vats, completely shutting off the access of atmospheric 

 oxygen. Under these circumstances the cells are able to develop their full 

 fermentative power and produce most alcohol. If the object to be attained 

 is not the fermentation of sugar but the growth of the yeast plant, as in 

 establishments for the preparation of ' pressed ' yeast, plentiful aeration must 

 be provided for. 



Theory of Fermentation and Putrefaction (HO). 



The fact that many fermentative processes take place in the absence of 

 oxygen would seem at first sight to give us some clue to the nature of the 

 phenomena. Comparisons have been drawn between fermentation and the 

 so-called ' intramolecular respiration ' of higher organisms. Intramolecular 

 respiration is a term applied by physiologists to the faculty possessed by 

 plants and animals of existing for a short time in an atmosphere devoid 

 of oxygen (pure hydrogen, for example), at the same time giving off CO 2 

 and forming in their tissues a minute quantity of alcohol. It seemed as 

 though all living substance were able to exist for a short time without 

 oxygen, splitting up respirable material (carbohydrates and perhaps albu- 

 mens) just as the Saccharomycetes do. The power of fermenting sugar would 

 indeed be only a special case of intramolecular respiration. 



We must not however forget that, even apart from purely oxidatory 

 changes such as the acetic fermentation, by no means all fermentative 

 processes are anaerobic. The work of the methane bacteria and of most 

 butyric organisms is indeed strictly anaerobic, but alcoholic fermentation, 

 although most vigorous in the absence of oxygen, is not arrested by the 

 presence of this gas, and most other fermentative processes are similar in 

 nature, i. e. they are facultative anaerobic. 



The term ' intramolecular respiration ' is intended to indicate a process 

 in which, although CO 2 is excreted, the oxygen is taken not from the 

 atmosphere, but from the complex molecules of the respirable substance 

 (e. g. sugar), which is broken up into the various less complex bodies we 

 call ' products of fermentation.' That such reductions do in fact take place 

 in anaerobic fermentation (e. g. butyric) may be proved by adding to the 

 fermenting fluid organic colouring-matters such as indigo or methylene 

 blue which become decolourized, that is to say they are converted into the 

 ' leuco ' compound with two additional atoms of hydrogen in the molecule. 



