VELOCITY OF REACTION 197 



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 varia- 

 tion in concentration of substratum. Also the effects of accumula- 

 tion of products of reaction must be avoided. Hence the ideal 

 condition is that in which there is excess of solid substratum, the 

 products of action are continuously removed by dialysis, and the 

 enzyme is present in constant strength throughout each experiment. 

 Such an arrangement as is suggested, for example, by Bayliss, of 

 a bell- jar filled 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 

 of substratum has been large and not very widely varied before 

 the measurement has been taken, and especially those in which, 

 where possible, a solid substratum has been employed. 



As Bredig has pointed out, the result would be more certain, 

 and more definite conclusions could be drawn if, in such experi- 

 ments, instead of measuring the different amounts of substratum 

 converted in equal times by varying amounts of enzyme, deter- 

 minations were made of the varying intervals of time necessary 

 to convert the same percentage of substratum as the concentra- 

 tion of enzyme is changed. For in the latter case whatever the 

 law may be governing the course of the reaction, and as we have 

 seen above this may be somewhat complicated, since the reaction 

 in such case runs to the same stage, in deducing the ratio of the 

 increases in velocity, due to the two different concentrations of 

 enzyme, this complicated factor eliminates out, being the same in 

 each case, and the ratio in the activation by the two quantities of 



