X PREFACE 



should not this messenger too have a hearing, as 

 well as religion and metaphysics? 



Perhaps the greatest differences between human 

 beings relate to their powers of constructive imagi- 

 nation, their ability to interpret the present and 

 predict the future in the light of the past. Most 

 persons do not possess such powers in high degree. 

 They are occupied with the struggle to get a living, 

 with reproduction, with eating and drinking and 

 dressing, and with certain banal amusements. An 

 interest in ideas for then* own sake is commonly 

 lacking. They take the static view of life rather 

 than the dynamic, whether it be in business or 

 politics or education. They fail fully to grasp the 

 idea that all things living are in a state of seething 

 flux, tending to construction or destruction. And 

 naturally they fail to see that the tendency, construc- 

 tive or destructive, is governed by quite definite 

 laws, which the human mind may in a degree under- 

 stand and even utilize. I foresee that to such minds 

 the point of view which has been presented in this 

 volume will make no favorable appeal, but will rather 

 prove distasteful or even repellent. 



The view of human problems which I have ven- 

 tured to present is one which has its origin in the 

 experiences and convictions of the student of biology 

 and of disease. In the first three chapters I have 

 tried to show in what respects the animal body may 

 be regarded as a mechanism, and in what respects 

 it differs from mechanical contrivances with which 



