90 CONCENTRATION OF ENZYME 



concentration, it is evident that as the optimum amount of acid 

 lies very little if any above O2 per cent., that there must, as in 

 the case of all other optimum points, be a considerable range in 

 acid concentration below this point throughout which change in 

 acid concentration has a very slight effect compared to what it 

 has at the lower and minimal concentrations of acid. Again, if 

 we take all the other factors in the formula except the time as 

 constant, the formula for amount of conversion and time becomes 

 S = K^/ t, now this is quite different from all the other formulae 

 deduced experimentally or theoretically for velocity of enzyme 

 reaction (see pp. 58-61). At the same time this casts a light upon 

 how under certain conditions such a formula can be obtained 

 empirically from experimental results, and can for a certain dis- 

 tance give an apparently close coincidence to the results of 

 experiment, and appear to give a law for expressing them, although 

 if under the conditions it were possible to carry the experiments 

 farther to either side, the law would be shown not really to exist. 

 For the above equation may be written, on squaring both sides, 

 S 2 = K 2 . t. This is the equation of a parabola, with its axis 

 horizontal, if the quantities converted are plotted as ordinates, 

 and the times as abscissae. Now, if the action of pepsin is similar 

 to that of trypsin as experimentally investigated by Bayliss, 

 instead of a parabola we should have first a straight line portion, 

 then a more or less logarithmic portion, and finally a portion where 

 the velocity of conversion fell off and finally became very small, 

 the line running almost asymptotic to the axis. But with the 

 exception of the initial straight line portion, which was probably 

 missed, and the later portion of the curve where the velocity is 

 falling off most rapidly, the intermediate portions of the two 

 curves are roughly parallel, and hence observations confined to 

 this region might easily give the impression that the law S = k^J t 

 gave the course of the reaction. 



The explanation of the " Schiitz law " is probably of a similar 

 nature, that is, it holds for a certain range only, and in this range 

 is an empirical law which gives an approximation to the truth. 



The writer considers this a more probable explanation than 

 the one given by Hober and F. Hofmeister, although this is very 

 ingenious. It will be remembered that when a substance dis- 

 sociates into two others in equal molecular concentration, the 

 equation for equilibrium runs c l = k c\, where c x is the concentra- 



