I si> PHYSIOLOGY 



substances will cause the amount of change in the unit of time to be reduced 

 to one-quarter of its previous amount. If now either a unimolecular or a 

 bimolccular reaction be quickened by the addition of a catalyser or ferment, 

 and the ferment enter into combination with one of the substances at some 

 stage of the reaction, it is evident that our equation must take account also 

 of the concentration of the ferment or catalyser. In the case of the catalytic 

 effect of molybdic acid on the interaction between hydrogen peroxide and HI, 

 there was definite evidence of a reaction taking place between the molybdic 

 acid and the peroxide, resulting in the formation of an intermediate compound, 

 namely, permolybdic acid. Erode has shown that the interaction of the molybdic 

 acid is revealed in the equation representing the velocity of the reaction. 

 Without the addition of niolybdic acid the equation would be : 



</>=K(C H2 o 2 X CHI). 



After the addition of molybdic acid, the equation becomes : 

 = K(C H ,,o 2 + 7 C molybdic acid)Cm, 



when 7 is another constant depending on the niolybdic acid. If ferments 

 act in a similar way by the formation of intermediate compounds, this fact 

 should be revealed by a study of the velocity at which the ferment action takes 

 place. 



Various methods may be adopted for the study of the. velocity of 

 ferment in action. If for instance, we are investigating the action 

 of diastase upon starch, we should take solutions of starch and of 

 diastase of known concentrations, keep them in a water bath at 

 38 C., and at a certain point add, say, 20 c.c. of ferment solution to 

 every 100 c.c. of the starch solution. At periods of five or ten minutes 

 after the addition had been made, 5 c.c. of the mixture might be with- 

 drawn by a pipette and at once run into boiling Fehling's solution. 

 The precipitated cuprous oxide would be dried and weighed, and 

 would give directly the amount of sugar formed by the action of the 

 ferment. After obtaining a series of data in this way, a curve could 

 be drawn, showing the amount of change of starch which had occurred 

 in each unit of time. In the case of the action of invertase on cane 

 sugar the investigation is still easier. Since the change from cane 

 sugar to invert sugar is accompanied by a change in the rotatory 

 power of the solution on polarised light, it is only necessary to put 

 the mixture of ferment and cane sugar into a polarimeter tube, which 

 is kept at a constant temperature by means of a water jacket, and 

 read off at intervals of a few minutes the change in the rotatory power 

 of the solution. From this change can be easily calculated the per- 

 centage of cane sugar still present, and therefore the total amount 

 which has been converted into fructose and glucose. 



In investigating the action of proteolytic ferments, as, e.g. that 

 of trypsin on caseinogen, samples are taken at five-minute intervals 

 and run into some substance such as trichloracetic acid, which will 

 precipitate all the unchanged protein, but will leave in solution the 

 products of hydration of the protein. From the amount of nitrogen 



