456 ENZYMES 



which act in quantities which bear no particular relation to the 

 weights of the reacting substances, are called catalytic agents. 



The process of catalysis has been defined by Ostwald as 

 " The acceleration of a chemical change by the presence of 

 some foreign substance," and it must be clearly understood 

 that a catalytic agent only accelerates a reaction, but is not 

 capable of bringing about a reaction which would not take 

 place at all in its absence.* Berzelius,t in 1850, drew attention 

 to the similarity between the decomposition of hydrogen per- 

 oxide, under the influence of insoluble inorganic catalysts 

 such as platinum or silver, and the decomposition of sugar into 

 alcohol and carbon dioxide under the influence of substances 

 known as ferments. Thus, in view of the ease with which so 

 many complex reactions are effected within the living organism 

 at a low, or a comparatively low, temperature, the idea is sug- 

 gested that nature likewise makes use of catalysts. 



As a matter of fact a large number of complex organic 

 substances, capable of exerting catalytic action, have been 

 isolated from plants and animals ; and to these substances the 

 name of enzymes has been applied. 



The food of plants, carbohydrate, protein, fats, etc., is, in 

 many cases, valueless unless it can be brought into a condition 

 suitable for assimilation and, very often, translocation. Thus 

 the starch in a leaf must be rendered soluble before it can be 

 transported to other parts of the plants, and, similarly, the 

 starch in a potato before it can be used for the nutrition of the 

 young shoots. 



In the living organism these changes are brought about by 

 the enzymes. 



With regard to the mode of the formation of enzymes 

 nothing is known ; they are generally described as being due 

 to the activity of the protoplasm, a phrase which contains 

 no information. Sometimes the enzymes are secreted in 

 specialized organs or in tissues more or less remote from the 



* Ostwald's definition, on various grounds, is not always accepted. 

 Thus Willstatter objects to its rigidity, and points out that the facts of 

 catalysis are so numerous and so diverse that it is futile to attempt to 

 explain all these phenomena by means of a single definition. 



t Berzelius: " Jahresber.," 1850, 15, 237, 240, 278. 



