PREFACE. 



/ T V HIS attempt to analyze the method em- 

 * ployed in the biological sciences arose 

 from the belief that the direct study of scientific 

 method, as it is illustrated by the works of the 

 accepted masters, is worthy of far more careful 

 attention than is usually accorded to it. As a 

 rule, scientific men are so deeply engrossed in 

 their investigations that they rarely undertake 

 to discuss method. The logical processes in- 

 volved and the nature of the difficulties met 

 w r ith in scientific investigation are the same as 

 in the practical affairs of life. The fundamental 

 processes of reasoning are the same everywhere ; 

 and it cannot but be helpful to study those pro- 

 cesses as they are actually applied by master 

 minds in fields where precision of method is 

 peculiarly essential. Even though there may 

 be grave question concerning the practical value 

 of the study of formal logic, there can be no 



