The Influence of Environment 291 



rising temperature which is also noticed in most life 

 phenomena. Thus Van Slyke and Cullen 1 found that 

 the reaction rate of the enzyme urease "is nearly 

 doubled by every io° rise in temperature between io° 

 and 50 . Within this range the temperature coefficient 

 is nearly constant and averages 1.91. From o° to io° it 

 is 2.80, from 50 to 6o° it is only 1.09. The optimum 

 is at about 55°." The rapid fall of the temperature 

 coefficient for enzyme action at the upper temperature 

 limit has been ascribed by Tammann to a progressive 

 destruction of the active mass of enzyme by the higher 

 temperature (by hydrolysis). This will, however, not 

 account for the high value of the coefficient near the 

 lower limit. But is it not imaginable that at low 

 temperature an aggregation of the enzyme particles 

 exists which is also equivalent to a diminution of the 

 active mass of the enzyme and that this aggregation is 

 gradually dispersed by the rising temperature? This 

 would account for the fact that at a temperature near 

 o°C life phenomena stop because the enzymes are all 

 in a state of aggregation or gelation; that then more 

 and more are dissolved and the rate of chemical re- 

 action increases since the mass of enzyme particles 

 increases until all the enzyme molecules are dissolved 

 or rendered active. Under this assumption three 

 processes are superposed in the variation of the value 



1 Van Slyke, D. D., and Cullen, G. E., Jour. Biol. Chem., 1914, xix. f 

 141. 



