VELOCITY OF REACTION 85 



deviations from the logarithmic law arise from the assumptions having 

 been made in the derivation of that law (1) that reversibility can be 

 neglected, and (2) that the intensity of action of the enzyme, per 

 molecule of substratum, can be taken as constant throughout the 

 reaction. 



EFFECTS ON VELOCITY OF REACTION OF ALTERATIONS 

 IN THE CONCENTRATION OF ENZYME 



The effects of variation in the amount of enzyme initially 

 added upon the velocity of reaction, in the case of the sucroclastic 

 enzymes and of trypsin, have been already mentioned in describing 

 the experiments upon the course of the reaction. Experiments 

 upon this question, to be comparable with one another, should be 

 made under such conditions that the concentration of the sub- 

 stratum remains constant throughout the experiment. Otherwise 

 the ratio of enzyme and substratum is continually varying during 

 the experiment, and the effect of variation in concentration of 

 enzyme is not obtained pure, but a combination of this with 

 variation in concentration of substratum. Also the effects of 

 accumulation of products of reaction must be avoided. Hence 

 the ideal condition is that in which there is excess of solid sub- 

 stratum, the products of action are continuously removed by 

 dialysis, and the enzyme is present in constant strength through- 

 out each experiment. Such an arrangement as is suggested, 

 for example, by Bayliss, 1 of a bell- jar rilled with solid gelatine 

 containing the enzyme and dialysing into a larger vessel (the 

 bell- jar being attached to one end of a lever which records the 

 rapidity of action by the loss in weight, and writes a record 

 on a smoked paper surface) would be an ideal arrangement for 

 such a purpose, on the supposition that the enzyme did not 

 dialyse out, as would probably be found to be realised within 

 the experimental limits, as the rate of dialysis of enzymes is 

 so slow. 



Such experiments have, however, not been yet carried out. 

 and the next best are those in which the observations have been 

 recorded at the initial stages of the reaction where the amount 



1 Loc. cit. 



