METHODS 21 



is a quantity that we know how to estimate with great 

 exactness. Now the biological phenomenon is very clearly 

 localized in the scale of temperatures ; we can assign a lower 

 and a higher limit of temperature, limits outside of which no 

 protoplasmic life can appear. It is very nearly between 

 and 60 Centigrade that all vital activities properly so 

 called are manifested, which does not mean that living 

 substances are inevitably killed outside of these limits ; on 

 the contrary, at least under certain forms, certain living sub- 

 stances can resist very rigorous cold and temperatures higher 

 than 100 Centigrade (212 Fahrenheit). This already 

 leads us to distinguish the property of " being alive " from 

 the property " able to live " ; the second is naturally more 

 elastic than the first. But vital activity properly so called 

 may be boldly placed within the limits of 60 Centigrade 

 and the neighbourhood of zero (freezing point). 



Without some little reflection on the real value of these 

 limits we might imagine that life occupies a large space in 

 the scale of temperatures ; we might even be astonished 

 that life begins almost identically with positive temperature. 

 The reason is that man, who is a living being, has chosen his 

 scale of temperatures for his own use and in accordance 

 with his own nature. He has taken as fixed points of his 

 scale the extreme points between which, under the pressure 

 familiar to him, water remains liquid ; 1 and it is quite 

 natural that life should be localized more or less between 

 the same fixed points, since protoplasm is a watery colloid 

 that needs liquid water for its existence. The whole history 

 of life is bound up with that of liquid water ; life is an aquatic 

 phenomenon. 



1 Waters having salts in solution have not the same freezing 

 temperature ; this is why we have to give zero as being only about 

 the lower limit which permits vital protoplasmic activities. 



