260 Mr. A. Compton. Optimum Temperature of an 



16 hours' incubation the tubes were withdrawn, the corks removed, and 

 each rapidly washed with 1 cm. 3 of water, the washings being carefully 

 added to the contents of the corresponding tube. The tubes were next 

 heated for five minutes in boiling water to stop the enzyme action, they 

 were then cooled, and the contents of each diluted to a known volume, such 

 that 20 cm. 3 of the diluted mixture corresponds to 36 mgrm. of maltose. 

 The proportion of maltose hydrolysed was estimated by the increase of 

 reducing power as determined by the method of Bertrand (ibid.). The 

 numbers obtained are recorded in Table II. 



If the percentage of maltose hydrolysed be plotted against the mean tem- 

 perature of the experiment these numbers give the series of curves 

 represented by fig. 1. 



Each curve shows a maximum at or about the same point, + 47°. Hence, 

 under the conditions of the experiment, the optimum temperature of the 

 ferment is constant, and independent of the variations in the concentration 

 of the substrate. 



That the optimum temperature is also independent of the concentration of 

 the enzyme is shown by the following experiments : — Four solutions of the 

 enzyme were prepared containing 10, 30, 60 and 100 mgrm. dissolved in 10 cm 8 . 



Fig. 1. Fig. 2. 



Fig. 1. — Substrate concentrations M/5 to M/30. Enzyme concentration 

 2 x 10~* grm. per cm.- 1 

 Fig. 2. — Substrate concentration M/20. Enzyme concentrations 2 x 10 -4 to 

 20 x 10~ 4 grm. per cm. 3 



