292 The Influence of Environment 



of Qio with temperature: (i) the supposed increase in 

 the number of available ferment molecules with in- 

 creasing temperature near the lower temperature limit ; 

 (2) the temperature coefficient of the reaction velo- 

 city which is nearly = 2 for io°C. ; (3) the diminution 

 of the number of available ferment molecules by hydroly- 

 sis or some other action of the increasing temperature. 

 This latter is noticeable near the upper temperature 

 limit. The reason that i and 3 interfere more strongly 

 in life phenomena than in the chemical reactions of 

 crystalloid substances may possibly be accounted for 

 by the fact that the enzymes and most of the con- 

 stituents of living matter are colloidal, i. e., consist of 

 particles of a considerably greater order of magnitude 

 than the molecules of crystalloids.^ 



We will now show the role of the temperature 

 coefficient upon phenomena of development. F. R. 

 Lillie and Knowlton'' first determined the influence of 

 temperature upon the development of the ^gg of the 

 frog and showed that it was of the same nature as that of 

 a chemical reaction. These experiments were repeated 

 a year later by 0. Hertwig.^ 



^ These considerations may meet the objections of Krogh to the 

 application of the van't Hoff rule of temperature effect on reaction 

 velocity to life phenomena. See also the discussion of this subject in 

 Kanitz's book. 



^ Lillie, F. R., and Knowlton, E. P., Zool. Bull., 1897, i. 



3 Hertwig, O., Arch, mikrosk. Anat., 1898, li., 319. See also E. 

 Cohen, Vortrdge fiir Aerzte uber pJiysikalische Chemie. 2d ed. Leip- 

 zig, 1907. 



