THE PRESIDENTS ADDRESS. 267 



which are consonant with its requirements as a living organism, 

 and its power of meeting emergencies as they arise is the 

 measure of its power to survive. Moreover, it is able to profit 

 by experience and to learn how best to overcome the difficulties 

 presented by its environment. This being so, we are justified in 

 maintaining that even the simplest living thing is endowed with 

 a certain degree of intelligence, for intelligence is nothing but 

 the power of learning by experience how to perform purposive 

 acts. 



We are not obliged, however, to suppose that the property 

 which distinguishes the living from the not-living intelligence, 

 vitality, or whatever we choose to term it came into existence 

 suddenly. It is more in accord w r ith our experience in other 

 directions to believe that it arose by imperceptible degrees, 

 pari passu with the evolution of organic from inorganic matter. 

 This, however, must not be taken to imply that there is no 

 essential difference between living and not-living bodies, either in 

 structure or behaviour. We might with equal justice say that, 

 because water is a compound of oxygen and hydrogen, there is 

 no essential difference between water and a mixture of these two 

 gases. We are told that to speak of the aquosity of water is 

 meaningless pedantry, and that to speak of the vitality of living 

 organisms is no less so. Of course, if such phrases are offered as 

 explanations of phenomena, they are entirely valueless ; but if 

 used merely as a kind of shorthand expression of the fact that 

 water and living organisms possess certain properties which dis- 

 tinguish them respectively from all other bodies, I see no more 

 harm in them than in any other technical descriptive terms. In 

 neither case can we supply a final explanation of the phenomena 

 to which we refer. 



Every stage in the evolution of matter is accompanied by the 

 development of new properties or qualities which require the use 

 of new descriptive terms. As to the so-called forces which lie 

 behind these properties w T e know nothing. We can only classify 

 them, as a matter of convenience, according to the effects which 

 they produce. We speak of the force of chemical affinity, of the 

 force of gravity, of electro-magnetic force, and so on ; and if 

 we choose to express our conviction that none of the so-called 

 chemical and physical forces are adequate to explain all the 

 phenomena of life, there is no logical reason why we should not, 



