PREFACE xvii 



tive cells of continuous and successive generations, as well as 

 in all the cells and tissues of the organism; and life environ- 

 ment: beginning with the monads and algae and ascending in a 

 developing scale of plants and animals. 



There are here four evolutions of energy rather than one, 

 and the problem of causes is how the four evolutions are ad- 

 justed to each other; and especially how the evolution of the 

 germ adjusts itself to that of the inorganic environment and 

 of the life environment, and to the temporary evolution of the 

 organism itself. 



I do not propose to evade the difficulties of the problem 

 of the origin and evolution of life by minimizing any of them. 



Whether our approach through energy will lead to the dis- 

 covery of some at least of the unknown causes of evolution 

 remains to be determined by many years of observation and 

 experiment. Whereas our increasing knowledge of energy in 

 matter reveals an infinity of energized particles even in the in- 

 finitely minute aggregations known as molecules — an infinity 

 which we observe but do not comprehend — we find in our 

 search for causes of the origin and evolution of life that we have 

 reached an entirely new point of departure, namely, that of 

 the physicist and chemist rather than the old point of departure 

 of the naturalist. We have obtained a starting-point for new 

 and untried paths of exploration which may be followed dur- 

 ing the present century — paths which have long been trodden 

 with a different purpose by physicists and chemists, and by 

 physiologists and biochemists in the study of the organism it- 

 self. 



The reader may thus follow, step by step, my own experi- 

 ence and development of thought in preparing these lectures. 

 The reason why I happened to begin this volume with the prob- 



