THE WONDER OF LIFE 533 



diphtheria and tetanus. Perhaps it is lacking in appropriate 

 physiological susceptibility to these diseases, without 

 having any special anti-toxin against them. 



It is in human nature to find satisfaction in fitness, and 

 not for practical reasons only, but because when things 

 ' fit ' we feel convinced of their rationality. It gave re- 

 assurance to the old lady to discover that so many great 

 rivers flowed past so many great towns, for that was as 

 it should be ; and it has often been pointed out that the 

 length of the day is physiologically well adapted to the 

 average man's capacity for work ! In his famous Bridge- 

 water Treatise (1834) Whewell showed in detail how the 

 constitution of the world from the length of the year 

 to the magnitude of the ocean, from the properties of water 

 to those of the atmosphere was admirably fitted for the 

 support of the vegetable and animal life which the earth 

 contains. And from of old it has been the delight of 

 naturalists to discover the adaptations with which organic 

 nature abounds. 



Some of those which we have been considering seem 

 almost magical in their intricacy and subtlety ; but most 

 intellectual combatants admit that Darwinism has supplied 

 a partially adequate formula for their coming-to-be. The 

 organism is always varying, always experimenting and 

 these variations or experiments (which we are still only 

 beginning to study) form the raw materials of organic 

 progress. They are subjected to Nature's sifting and 

 singling, pruning and favouring (' Natural Selection in the 

 Struggle for Existence '), and the result is the establish- 

 ment of the adaptations we justly admire. The magicalness 

 has gone ; the rationality is more apparent than ever. 

 And if we can more or less clearly see how individual 



