Inside of these upper and lower temperature limits we find that life phenomena are influenced by temperature in such a way that their rate is about doubled for an increase of the temperature of 10° C., and that this temperature coefficient for 10°, Q₁₀, very often steadily diminishes from the lower to the higher temperature; so that near the lower temperature limit it becomes often considerably greater than 2 and near the higher temperature limit it becomes very often less than 2.[249] This influence of temperature is so general that we are bound to associate it with an equally general feature of life phenomena; and such a feature would be most likely the chemical reactions. It is known through the work of Berthelot, van’t Hoff, and Arrhenius that the temperature coefficient for the velocity of chemical reactions is also generally of about the same order of magnitude; namely ≧2 for a difference of 10°. In chemical reactions there is also a tendency for Q₁₀ to become larger for lower temperature, and coefficients of Q₁₀ about 5 or 6 have repeatedly been found for purely chemical reactions between 0° and 10°, _e. g._, for the inversion of cane sugar by the hydrogen ion. The temperature coefficient for the reaction velocity of ferments shows the same diminution of Q₁₀ with rising temperature which is also noticed in most life phenomena. Thus Van Slyke and Cullen[250] found that the reaction rate of the enzyme urease “is nearly doubled by every 10° rise in temperature between 10° and 50°. Within this range the temperature coefficient is nearly constant and averages 1.91. From O° to 10° it is 2.80, from 50° to 60° 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 0°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 reaction 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 of Q₁₀ with temperature: (1) the supposed increase in the number of available ferment molecules with increasing temperature near the lower temperature limit; (2) the temperature coefficient of the reaction velocity which is nearly =2 for 10°C.; (3) the diminution of the number of available ferment molecules