CHEMICAL CHANGES IN LIVING MATTER. FERMENTS 175 



Of these, all which involve a splitting of a large molecule into smaller 

 ones with the taking up of one or more molecules of water, as well as, 

 in all probability, those in which the reverse change of dehydration 

 and synthesis occur, are effected in the body by means of ferments. 

 To the same agency are also ascribed the process of deamination, 

 which takes place in many organs of the body, and, though with less 

 certainty, the processes which involve decarboxylation. 



FERMENTS 



Under the name ferments we include a number of substances of 

 indefinite composition whose existence is chiefly known to us by 

 their action on other substances. A ferment has been denned as a 

 body which on addition to a chemical system is able to effect changes 

 in this system without supplying any energy to the reaction, without 

 being used up, and without taking any part in the formation of the 

 end products. It differs therefore from the reacting substances in 

 the absence of any strict quantitative relationships between it and 

 the substances included in the system in which its effects are produced. 

 Minimal quantities of ferment can induce chemical changes involving 

 almost indefinite quantities of other substances, the only result oj in- 

 creasing the quantity of ferment being to quicken the rate of the change. 

 Since they are effective in minimal doses they occur in living tissues 

 in minute quantities, and it is partly due to this fact that it has hitherto 

 proved impossible to obtain any preparation of a ferment which could 

 be regarded as a pure substance. The difficulty in their isolation 

 is increased by the fact that all of them are colloidal or semi- 

 colloidal in character, and present, therefore, the tendency common to 

 all colloids of adhering to other colloidal matter as well as to surfaces 

 such as those presented by a precipitate. A common method of isolat- 

 ing, or rather obtaining a concentrated preparation of a ferment is to 

 produce in its solution an inert precipitate such as cholesterin or 

 calcium phosphate. The ferment is carried down on the precipitate 

 and may be obtained in solution on washing the precipitate with 

 water. A further difficulty in their preparation lies in the unstable 

 character of many members of the group. Although they are not 

 coagulated by alcohol, they are nevertheless gradually changed, so 

 that every act of precipitation of a ferment tends to rob it of some of 

 its powers, i.e. of the only characteristic by which we can establish 



its identity. 



Of these ferments a large number have already been described 

 as taking part in the ordinary chemical processes of life. So wide 

 is their dominion in cell chemistry that many physiologists have 

 thought that the whole of life is really a continual series of ferment 

 actions. The following list represents some of the ferments whose 



