3 r8 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



molecule, forming a substance which can be isolated, and is known as 

 ethylsulphovinic acid ; and that this compound then reacts with another 

 molecule of alcohol, forming ether and regenerating the sulphuric acid 

 molecule, which is then free to repeat the process, and can be made to 

 do so indefinitely. 



This action may be represented thus : 



(1) C 2 H 5 .O.H + : j S0 4 = H.O.H + C A SO 4 



(alcohol, sulphuric acid) (water, ethylsulphovinic 



acid) 



(2) C A S0 4 + C 2 H 5 .OH = I S0 4 + ^ 



(ethylsulpho- (alcohol) (sulphuric (ether) 



vinic acid) acid) 



Another good example of such an interaction is that of the alternate 

 formation of a higher oxide of nitrogen (N 2 3 ) from a lower (NO), and 

 then the regeneration of the lower oxide, which is said to occur in the 

 formation of English sulphuric acid; the oxygen taken up in each 

 cycle going to form, with sulphur dioxide and water, sulphuric acid; 

 while, as a net result, the nitric oxide remains unchanged, and may take 

 action again and again until it is dissipated by diffusion or otherwise. 1 



Such a part the enzyme may take in a ferment action ; a molecule 

 of it may unite with a molecule of the substance undergoing digestion. 

 Thus an unstable compound may be formed; the elements of a water 

 molecule may combine with those of the fermentable substance, forming 

 a new substance ; while the ferment is regenerated to undergo another 

 cycle. Of all this, however, there is no experimental evidence ; there 

 is only the analogy, and analogies are sometimes misleading. 



Besides these reactions, there are others in which the action of the 

 catalytic agent is, almost undoubtedly, merely a physical one ; that is to 

 say, in which the catalytic agent does not combine with the catalysed 

 substance, and then become regenerated. Such an action, for example, 

 is that of a trace of iodine in converting amorphous into red 

 phosphorus. Here the amount of iodine required is too excessively 

 small to suppose that it combines with phosphorus in one form and 

 yields it up in the other. The supposition is more probable that the 

 iodine finds the phosphorus in an unstable state, and in some fashion 

 enables it to do that which it already has a tendency to do, namely, swing 

 into stability. Such a reaction, only still more physical in character, 

 is found in the case of exceedingly unstable compounds (such as 

 detonating substances), where mere mechanical percussion, most probably 

 by producing molecular vibration, causes a chemical reaction to take 

 place with great rapidity. It is very likely that in many cases, 

 especially those in which the catalytic agent is merely required to 

 be present in traces, that there is no intermediate substance formed, 

 and that the catalytic agent acts in a physical manner, inducing a 

 compound already unstable to pass into a more stable condition. It 

 is not even necessary that the substance should be unstable in the 

 usual sense of the word, but only that the new products should be 



1 A similar oxygen-carrier, of oxygen to be used in tissue metabolism, is found in 

 haemoglobin, which may be looked upon as a catalytic agent, taking up oxygen, parting 

 with it to bring about a reaction, the details of which we do not know, and so becoming 

 regenerated and coining out of the total process unchanged. 



