xvi INTRODUCTORY LETTER TO SENATOR MOSSO 



and defensible one for a scientific man to occupy, 

 who is loyal to the spirit of research. We may then 

 assume with little risk of mistake that no hypothesis 

 of life yet offered requires serious scientific consider- 

 ation. A confession of agnosticism is here a positive 

 contribution to the truth. On the other hand, there 

 is no reason for giving up the endeavour to get 

 nearer to the final goal of biology because attempts 

 to reach it by the short cut of speculation have always 

 failed. Indeed, at the present time much work is 

 being done towards answering general questions, the 

 answers to which appear necessary preliminaries to 

 attacking the problem of life itself. 



Before the American Association for the Advance- 

 ment of Science, in 1879, I read a paper " On Condi- 

 tions to be Filled by a Theory of Life," which was 

 published in abstract only. 1 It contained an enumera- 

 tion, as complete and exact as I could make it, of 

 phenomena which any tenable hypothesis of vitality 

 must explain ; the effort being made to generalise the 

 statements to the farthest legitimate scientific limit, 

 thus reducing as far as possible the number of phe- 

 nomena. The result was a very vivid impression on 

 my mind of the inadequacy of. all hypotheses of 

 vitality, and that impression is to-day undisturbed. 

 Had circumstances permitted I should have devoted 

 myself entirely to the study of general problems, but 

 necessity early led me into teaching embryology, and 

 in the acquisition of even my partial mastery of that 



This abstract is reprinted as Appendix V to this volume. 



