84 THE CHEMISTRY OF CATTLE FEEDING 



also of other cases, and, as has been said, possibly in all ; but 

 there are many fermentations which have not, so far, been 

 observed to occur except in the presence of living organisms. 



In some fermentations the changes take place outside the 

 cells, and in others within it. In the former case, the enzyme 

 produced by the organism is probably excreted into the fer- 

 menting liquid. In the latter, the fermentable substance is 

 probably absorbed into the cells of the organism, and the sub- 

 stances produced by the action of the enzyme in the cell are 

 excreted into the liquid. 



Enzymes such as diastase, pepsin, etc., are sometimes 

 called unorganised or formless ferments, in contradistinction 

 to the organised or living ferments such as yeast, bacteria, 

 etc., which, of course, are cellular plants. 



It is difficult to understand the part played by the organ- 

 isms in those changes which are apparently due to their direct 

 action, even when the chemical nature of the change is known. 

 Fermentations due to the action of enzymes we may hope 

 ultimately to unravel, however obscure and complex they may 

 be, as they are probably ordinary chemical reactions resulting 

 from the action of the enzymes on the fermented substances. 

 It is characteristic of these changes that the ferments them- 

 selves remain apparently unaltered, and relatively small 

 amounts can therefore cause the transformation of practically 

 unlimited quantities of the substance. 



Many similar or analogous reactions are familiar to all 

 students of chemistry, e.g. the oxidation of sulphur dioxide by 

 oxides of nitrogen, which act as carriers, the etherification of 

 alcohol, various catalytic reactions, and the hydrolysis of 

 bihexose sugars and amyloses (pp. 21, 26) by dilute acids. 

 The last is peculiarly apposite, because the same result, pro- 

 duced by the action of enzymes, is often regarded as a typical 

 fermentation. 



In the process of etherification, the sulphuric acid com- 

 bines with the alcohol, and, by a secondary reaction, it is 

 again regenerated according to the equations 



(1) C 2 H 5 OH + H 2 S0 4 -> C 2 H 5 HS0 4 + H 2 O 



(2) C 2 H 5 HS0 4 -f- C 2 H 5 OH - (C 2 H 5 ) 2 O + H 2 SO 4 



