22 THE NATURE AND ORIGIN OF LIFE 



Nowadays we can obtain in laboratories temperatures 

 far lower and far higher than those known to our ancestors ; 

 we can also recognize in certain stars the existence of tempera- 

 tures higher even than that of the electric furnace. Hence 

 life, limited to the temperature of liquid water, appears to 

 occupy in the scale of temperatures as restricted an interval 

 as it does in the scale of magnitudes. 



In order that life should exist on the earth's surface, the 

 latter must have limits of temperature very exactly fixed. 

 This is why life has not always existed on the earth. It 

 could appear there only when the surface temperature 

 had become low enough for water to be liquid ; it cannot 

 endure when the temperature becomes too low. Life is 

 only a surface accident in the history of the thermic evolu- 

 tion of the globe. 



This question of temperature is essential in all that 

 concerns phenomena which, like vital phenomena, com- 

 prise chemical activities. We know, indeed, that chemical 

 reaction between two given compound bodies takes place 

 only at a certain temperature ; under different conditions 

 it may not take place at all, or even turn out just the con- 

 trary. Now we have seen that a very important character 

 of living colloids seems to consist in the fact that there is 

 a relation of cause and effect between the colloidal equili- 

 brium of these substances and the chemical equilibrium of 

 their constituent parts. With these particular chemical 

 constituents, therefore, the conditions of existence have to 

 be such, at the temperature of life, that slight variations 

 in the colloid state (electrostatic state, hydrostatic state, etc.) 

 may intervene to set up chemical reactions among these 

 constituents, or even to change the direction of reactions 

 already existing. In other words, in the thermic conditions 

 of protoplasmic life, at least a certain number of the chemical 



