ARTICLES 419 



inco-ordinated facts and theories which exists at present must 

 be left for the future to unravel. 



Temperature. — ^The effect of temperature in increasing the 

 velocity of enzyme action is most constant, and is even more 

 marked than the effect of heat in chemical reactions. In 1910 

 Mendel and Blood brought forward a most striking instance of 

 the effect of heat. They found that papain at 80° C. digests 

 almost three times as much excelsin in fifteen minutes as it does 

 in seventeen hours at 44° C. In explanation of this phenomenon 

 the work of Caesana (191 3) has already been referred to under 

 " Dispersion." It is also to be noted that the work of Euler 

 and Beth of Ugglas (1910) showed that the temperature co- 

 efficient of inversion by invertase and maltase is higher than 

 that of inversion by acids. 



Although enzymes show an optimum temperature, the 

 majority are destroyed by extreme heat — e.g. boiling — and it 

 has been suggested that the destruction is due to action on the 

 complex colloidal system. When enzyme is adsorbed, how- 

 ever, it is not so easily destroyed. This was noted by Bayliss 

 (191 1 ), who investigated the point, using trypsin and charcoal. 

 Similar protection has been shown in regard to invertase and 

 cane sugar. It may here be noted that when the temperature 

 coefficient of urease on urea was worked out by Van Slyke and 

 Cullen, they found it to be that of a chemical reaction rather 

 than that of a physical combination. 



The work of Albert and Alexandre Mary (191 8) has been 

 referred to already. These investigators, it will be remem- 

 bered, concluded that the temperature inactivation of natural 

 enzymes was undoubtedly due to a degradation of their dis- 

 persed phase. This increase of enzyme action by temperature 

 gives a simple explanation of the effect of heat on muscle 

 activity, and Moore (191 8), working with the embryo heart of 

 Fundulus, shows that the rate of heart beat due to heat follows 

 a similar curve to that of the velocity of an enzyme reaction as 

 affected by temperature. The recent work on the physiology 

 of catalase and its importance in the activity of the body 

 mechanisms would tend to support this explanation. 



Effect of Products. — ^As is common to so many processes in 

 nature, the products of reaction may have an effect on the 

 velocity with which the reaction proceeds. In the case of 

 enzymes in nature, however, the products of the reaction are 

 absorbed or are passed on to another part of the body. This 

 interference therefore is more clearly seen in vitro, and is dis- 

 tinctly observed when the products have an opposite reaction 

 to that of the medium in which the enzyme exercises its effect. 

 Thus Van Slyke (19 14) shows that urease is inhibited by 

 ammonia, a product of its decomposition of urea. Much of the 



