CATALYSIS AND ENZYMES 307 



process. When a metal in mass is immersed in acid, the diffusion process is slower 

 than the chemical reaction. 



When one substance is adsorbed on the surface of another, it does not follow 

 of necessity that any chemical reaction will occur. Aniline on the surface of 

 mercury in Lewis' experiments (1910, 3) may be given in illustration. When 

 chemical reaction does occur, the rate at which it proceeds is obviously controlled 

 by the amount adsorbed at any given moment, so that an exponential relation 

 between the concentration and the velocity is to be expected. 



The mode of action of catalysts, with especial reference to enzymes, will be 

 discussed later. 



ENZYMES AS CATALYSTS 



We have seen that certain substances, extracted from animals and plants, act in 

 a catalytic way similar to that in which an inorganic compound, such as acid, does. 

 These substances are known as "enzymes " or "ferments." 



In the discussion of their properties, certain names will have to be used, so that the 

 terminology of the subject must first be referred to. The choice of correct words is really 

 more than a mere matter of convenience. If the word used has a meaning, is connotative, 

 it should tell us something about the thing named, although it frequently happens that the 

 original meaning becomes changed as knowledge increases. As often pointed out, the progress 

 of a science depends much on the language used in the description of its phenomena. It 

 is a mistake, however, to be hasty in inventing new names ; more care must be exercised 

 in attaining certainty that the new name is required to describe phenomena of a new kind, 

 inadequately provided for by names already in use. Numerous names, at one time thought 

 necessary, have disappeared. 



As various substances were extracted from organisms, and the similarity of the 

 action of these substances to that of alcoholic fermentation became obvious, it was 

 natural to call them "fei'ments." And when Cagniard de Latour (1838) showed 

 that alcoholic fermentation was due to a living organism, substances such as the 

 "diastase," precipitated by Payen and Persoz (1833) from extracts of malt, were 

 distinguished as " soluble," " unorganised," or " unformed " ferments from " living," 

 "organised," or "formed" ferments. In process of time some confusion was 

 caused by this double use of "ferment," so that Kiihne (1878, p. 293) thought it 

 well to introduce a new name for the soluble, or unorganised ferments. The 

 passage is sufficiently interesting to be translated here : 



"The latter designations (formed and unformed ferments) have not gained 

 general acceptance, since on the one hand it was objected that chemical bodies, like 

 ptyalin, pepsin, etc., could not be called ferments, since the name was already 

 given to yeast cells and other organisms (Briicke) ; while, on the other hand, it was 

 said that yeast cells could not be called ferment, because then all organisms, 

 including man, would have to be so designated (Hoppe Seyler). Without stopping 

 to inquire further why the name excited so much opposition, I have taken the 

 opportunity to suggest a new one, and I give the name enzymes to some of the 

 better known substances, called by many ' unformed ferments.' This name is not 

 intended to imply any particular hypothesis, it merely states that cv typi) (in yeast) 

 something occurs that exerts this or that activity, which is supposed to belong to 

 the class called fermentative. The name is not, however, intended to be limited to 

 the invertin of yeast, but it is intended to imply that more complex organisms, 

 from which the enzymes, pepsin, trypsin, etc., can be obtained, are not so 

 fundamentally different from the unicellular organisms as some people would have 

 us believe." 



On account of the important work done by Kiihne in the elucidation of the 

 action of enzymes, I introduce his portrait in Fig. 83. The name " enzyme " has 

 come into general use, although " ferment " is still to be met with as synonymous 

 with it ; while the application of this name " ferment " to living organisms has 

 dropped out of use. 



Enzymes may be shortly denned as the catalysts produced by living organisms. 

 If we grant that the substances known by the name are a special kind of catalysts, 

 which we have still to show, it is clear that the introduction of a name for them 

 is merely a matter of convenience. At the same time, the majority of them have 



