62 EXPERIMENTAL OBSERVATIONS ON 



which, the catalyst acts is present, to the end-point at which the 

 substratum has been as completely converted into the products 

 of reaction as is possible under the conditions of experiment ; 

 (2) those in which the effects upon the velocity of varying the 

 concentration (a) of ferment and (b) of substratum are observed 

 in the earlier stages of the experiment ; and (3) those in which 

 the effects of addition of one or other of the products of reaction 

 at the initial stage are studied, or the effect of addition or removal 

 of such products upon the end-point or apparent equilibrium 

 point of the reaction. The experimental measurement in all 

 cases is that of the quantity or percentage of the substratum con- 

 verted in a given time, and this has been measured in many 

 different ways. The enzymes which have been most employed 

 have been those which act upon starches or sugars, that is, the 

 amyloclastic and ucroclastic enzymes in the terminology of H. E. 

 Armstrong, 1 but recently an important paper has been communi- 

 cated by Bayliss on the velocity of reaction caused by trypsin 

 in different proteid solutions. Determinations of the rate of 

 change in the sugar solutions have been made chiefly by 

 the polarimeter, but estimations by various modifications of 

 Fehling's method have also been employed. In the case of 

 trypsin, Bayliss has used the method of determining change in 

 electrical conductivity. 



The results of experiment may be stated either in the form 

 of a curve in which the co-ordinates represent time from the com- 

 mencement of the experiment and percentage of substance con- 

 verted, or by calculating the values of the constant of reaction (k) 

 at each period at which a determination is made. 



The velocity of reaction induced by inorganic catalysts, and 

 particularly by acids and alkalies, has been the subject of many 

 researches which cannot here be reviewed. It must suffice to 

 state that the results follow fairly closely the formulse deduced 

 above, as shown by the close values obtained throughout the 

 experiment for the value of the constant of reaction deduced on 

 the basis of the formula. 



1 It is pointed out that the older terminology, amylolytic, &c., is open to con- 

 fusion with electrolytic, hydrolytic, &c., because amylolytic meant that the 

 starch is split up, while electrolytic does not mean a spliting up of electricity 

 but by means of electricity, hence the author suggests the more rational 

 terms, amyloclastic, &c. 



