TERMINOLOGY 75 



not, however, in reality, affect the reasoning, since the reactions 

 can be enormously accelerated by other bodies, which act as addi- 

 tional catalysts and may be investigated independently. It is, in 

 fact, a matter of considerable difficulty to discover a slow reaction 

 which is definitely known to take place in the complete absence of 

 any catalyst. 



"Moreover, it must not be forgotten that, as J. J. Thomson and 

 others believe, a catalyst may possibly start a reaction. This is 

 not, theoretically, in disagreement with the view taken by 

 Ostwald. To return to our mechanical illustration, the ' friction' 

 between the weight and the glass plane may be sufficiently great 

 to prevent movement altogether, until oil is applied. But the use 

 of the name 'friction' implies the idea of movement and the exist- 

 ence of forces tending to produce it. One may indeed suppose 

 that the weight actually does move for an infinitesimal distance, 

 but is at once arrested by the resistance met with. From thi? 

 point of view the definition of a catalyst would be expressed some- 

 what thus : A substance which ch anges the rate of a reaction which 

 is actually in progress, or which is capable of proceeding without 

 any supply of energy from without, if certain resisting influences 

 are removed. The difference between diminution of friction by 

 oil and the removal of a catch is that, in the former case the action is 

 continuous throughout the fall of the weight, whereas in the latter 

 case the action is only momentary, at the commencement of the 

 fall, on the rate of which it has no further effect." 



Terminology. Within recent years attempts have been made to 

 systematize the terminology used in referring to enzyme action. 

 The name of the substance on which the enzyme acts is called 

 substrate. 



As to the names of the enzymes themselves it is customary to 

 use the termination " ase" which denotes an enzyme and this 

 termination should be added to the root of the word which names 

 the substrate; for example, lactase is the enzyme accelerating the 

 hydrolysis of lactose, sucrase of sucrose, maltase of maltose, etc. 

 Unfortunately, in many cases old names have become so fixed that 

 it is not desirable to replace them, as, for example, pepsin for the 

 acid proteinase and trypsin for the alkali proteinase. At other 

 times the enzymes are incorrectly named from the simpler substance 

 in place of the more complex substrate; for example, invertase for 

 the ferment which inverts sucrose. 



It is the custom with many writers to speak of the enzymes which 

 attack, say, starch or protein, as "amylolytic" or "proteolytic," 

 respectively; but Armstrong has pointed out that these names 

 are incorrectly formed. "Amylolytic" in analogy with "electrolytic" 

 should mean a decomposition by means of starch. To avoid this 

 misuse of words he advocates the use of the termination " clastic" 



