NATURE OF THE CHEMICAL CHANGE. 319 



more stable ; or, in other words, that there should be energy set free in 

 the process of change. 



In ferment action, the chemical energy of the resulting products 

 is always less than that of the substances from which they were formed ; 

 this is shown by the heats of combustion of the end products amounting 

 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 be 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 ; ISTencki, Journ. 

 f.prakt. Chem., 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. 



