6 PREFACE. 



far along the road toward its completion that a 

 review of the progress made and a glance at the 

 yet unexplored realms and unanswered questions 

 will be profitable. For this purpose this work is 

 designed, with the hope that it may give a clear 

 idea of the trend of recent biological science and 

 of the advances made toward the solution of the 

 problem of life. But the limitations of science are 

 indicated in the concluding General Summary. 



