3 rS CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
molecule, forming a substance which can be isolated, and is known as 
ctlnlsulphovinic 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 + \ S0 4 = H.O.H + C A S0 4 
(alcohol, sulphuric acid) (water, ethylsulphovinic 
acid) 
(2) °*^ 5 S0 4 + 2 H 5 .OH = ** SO, + ^ 2 2 s ' 
(etlrylsulpho- (alcohol) (sulphuric (ether) 
viuic 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 shotdd 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 coming out of the total process unchanged. 
