158 PHYSIOLOGY 



Many other ferments will probably be distinguished with increase in 

 our knowledge of cellular metabolism. The long list which is here given 

 suffices to show how great a part these bodies must play in the normal 

 processes of life. - A study of the conditions of ferment actions is therefore 

 essential if we would form a conception of the chemical mechanisms of the 

 living cell. 



It is important to note that all the changes wrought by ferments can 

 be effected by ordinary chemical means. Thus the disaccharides can be 

 made to take up a molecule of water and undergo conversion into mono- 

 saccharides. If a solution of maltose be taken and bacteria be excluded 

 from the solution, it undergoes at ordinary temperatures practically no 

 change. If the solution be warmed, a slow process of hydraticn takes place 

 which is quickened by rise of temperature, so that if the solution be heated 

 under pressure to, say, 110 C., hydrolysis occurs with considerable rapidity. 

 If however a little maltase be added to the solution, the change of maltose 

 into glucose takes place rapidly at a temperature of 30 C. In the same 

 way a solution of protein may be kept almost indefinitely without undergoing 

 hydrolysis, which however can be induced by heating the solution under 

 pressure. The action of the ferments in these two cases is to quicken a 

 process of hydrolysis which without their presence would take an infinity 

 of time for its accomplishment. 



In this respect their action is similar to that of acids, and indeed of a 

 whole class of bodies which are spoken of as catalysers or catalysts. A 

 catalyser is a substance which will increase (or diminish) the velocity of a 

 reaction without adding in any way to the energy changes involved in the 

 reaction, or taking any part in the formation of the end-products. Since 

 the catalyser is unchanged in the process, a very small quantity is able to 

 influence reactions involving large quantities of other substances. By 

 adding acids to a watery solution of the food-stuffs, the process of hydrolysis 

 is quickened in proportion to the strength and concentration of the acid. 

 The effective catalytic agents in this process appear to be the hydrogen ions 

 of the free acid. There are many other bodies, besides the free acids, which 

 may act as catalysers, and a study of the conditions under which catalysis 

 takes place may throw some light on the essential nature of the action of 

 ferments. 



The velocity of almost any reaction in chemistry can be altered by the 

 addition of some catalytic agent, and there are few of the ordinary reactions 

 in which catalysis does not play some part. Among such processes we may 

 instance the action of spongy platinum on hydrogen peroxide. Hydrogen 

 peroxide undergoes slow spontaneous decomposition into water and oxygen. 

 If a little spongy platinum be added to it, it is at once seen to decompose 

 rapidly with the evolution of bubbles of oxygen, and the action does not 

 cease until the whole of the hydrogen peroxide has been destroyed. Spongy 

 platinum is able in the same way to quicken a very large number of chemical 

 reactions. Thus sulphur dioxide and oxygen when heated together will 

 combine very slowly ; the combination becomes rapid if a mixture of the 



