NATURE OF THE CHEMICAL CHANGE. 319 
more stable; or, in other winds, that there should be energy set free in 
the process of change. 
In ferment net inn, the chemical energy of the resulting products 
is always less than that of the suhstanees from which they were formed; 
this is shown by the heats of combustion of the end products amoivnting 
to less than those of the initial products. 
The action of ferments is hence in all respects analogous to that of 
catalytic agents ; there is a passage from a less stable to a more stable 
condition, which is brought about by an agent which is not itself altered 
in the process. 
The two principal hypotheses are then — (1) That the enzyme 
combines with the substance on which it is acting, and that the unstable 
compound so formed decomposes, yielding the new substance and 
regenerating the enzyme ; (2) that the enzyme is in a state of molecular 
movement, which induces a molecular movement in the fermentable 
substance, or increases such a movement when already present, so that 
the molecule breaks up, over-swings, or over-vibrates as it were, into a 
more stable condition, so giving rise to new substances. 
Nature of the chemical change. — Somewhat more is known of the 
nature of the chemical changes induced by the ferments than of the 
mode in which they bring about such changes. It is probable that in 
all cases ferment action is accompanied by hydrolysis, i.e. the taking 
up of the elements of water. 1 This is known with certainty to be the 
case in all actions of diastatic and inverting ferments, and is very pro- 
bably true also for proteolytic ferments. This subject will be considered 
more in detail in treating of the specific action of the various enzymes 
on the different classes of foodstuffs ; reference will only be made here 
to the general arguments which go to show that such a process of 
hydrolysis is a universal accompaniment of ferment action. 
1. In many cases the composition of the products of the fermentation 
compared with that of the initial substance shows directly a taking up 
of water. In those in which this is not so, carbonic anhydride is usually 
one of the constituents, and if this be considered as united with the 
elements of a water molecule to form carbonic acid, as it probably is 
when formed in the reaction, water is taken up here also. In all cases, 
however, whether the products of the reaction directly show the taking 
up of water or not, the presence of water is essential to the reaction, 
for no ferment is known which will act otherwise than in the presence 
of water. 
2. Again, the action of any of the ferments may lie closely imitated 
by the action on the several fermentable or digestible materials of 
dilute acids or alkalies, and these are recognised throughout the domain 
of organic chemistry as the most powerful hydrolytic agents known. 
3. It has been shown that in the case of coagulation by fibrin ferment 
an increase of weight of dried material takes place, probably due to the 
elements of water being taken up in the process. This was demonstrated 
by taking two equal portions of plasma, allowing one to clot and not the 
other, and then drying both under similar conditions, when the clotted 
sample was found to weigh a half per cent, more than the other. 2 
1 Hoppe-Seyler, Arch. f. d. ges. Physiol., Bonn, 1876, Bd. xii. S. 1 : Xemki, Journ. 
f.prakt. Chcm., Leipzig, 1879, Bd. xvii. S. 105. 
2 Observation by A. Schmidt, communicated by G. Tamman, Ztschr. f. physiol. Chem., 
Strassburg, 1892, Bd. xvi. S. 271. 
