94 INFLUENCE OF TEMPERATURE 



the diastatic ferments of the liver and pancreas are not de- 

 stroyed by boiling in alcoholic solution, and Fermi and Pernossi 

 find that enzymes are only slowly acted upon in amyl alcohol 

 solutions. 



In the dried condition it has been shown that enzymes can 

 be heated td as high as 160 0. without losing their activity. 



Exposure to low temperatures does not appear to have any 

 marked effect upon enzymes. 



With regard to the effect of alterations of temperature upon 

 the rapidity of action of ferments, it is found that each ferment 

 is most active at a temperature called the optimum temperature, 

 which varies in the case of each ferment, and also in the same 

 ferment with the conditions of solution, presence of neutral salts, 

 reaction, and temperature to which the solution has previously 

 been exposed. As a general rule the optimum temperature lies 

 between 35 and 45 C., but according to Roberts the action of 

 trypsin increases even up to 60 C., at which temperature it is 

 however rapidly destroyed. 



It is stated by Bredig that the existence of the optimum 

 temperature and the decrease in rapidity of reaction at higher 

 temperatures than the optimum is due to two opposing factors. 

 The first factor is the increase in reaction velocity which rise in 

 temperature always occasions, and the second is the destruction 

 of a portion of the enzyme which gradually occurs, more rapidly 

 as the temperature is increased, and finally outbalances the 

 positive effect due to increased temperature per se. Ernst working 

 in Bredig' s laboratory tested the rate of action of Bredig's platinsol 

 upon water-gas, and found conformably to this view that it also 

 possessed an optimum temperature of action, the exact position 

 of which varied with the previous history of the platinsol, the 

 period during which it had been kept at the higher temperature 

 previously to starting the reaction, &c. 



Accordingly it would appear that the optimum temperature 

 is not a peculiar characteristic of enzymes, but depends upon their 

 instability at the optimum temperature and above it. It must 

 be added, however, that in presence of their appropriate substrata, 

 some ferments are very stable at their temperature of optimum 

 activity, e.g. pepsin, the rate of destruction being practically 

 inappreciable, and hence it appears to the writer that although 

 Bredig's view may hold in some cases it is not a universal ex- 



