x PREFACE 



departments of science have so multiplied that 

 hardly any facts or theories which come within 

 the scope of this work are inaccessible to the 

 general reader. On the other hand, it has 

 been deemed necessary to explain every sub- 

 ject as it has arisen, for many of the readers 

 of this volume will perhaps be unfamiliar even 

 with the rudiments of all the departments of 

 science which have necessarily been touched 

 upon. 



Much of the content of the following pages 

 has already been set forth in lectures. The 

 general conclusion was presented last February 

 to the members of the Harvard Seminary of 

 Logic ; later in the academic year I delivered 

 the substance of the book as part of a college 

 course to my students of biological chemistry 

 in Harvard College. 



I am indebted to many of my colleagues in 

 Harvard for valuable assistance, criticism, 

 and expressions of opinion. Without such 

 assurances that I have not fallen into gross 

 blunders, and that the conclusions appear rea- 

 sonable to experienced men of science, I should 

 not have dared to undertake a task which 

 overtaxes my knowledge, or positively to as- 

 sert a proposition which is in conflict with 

 much of the scientific thought of the last half 

 century. Especial thanks are due to Professor 



