THE PASTEUR INSTITUTE 181 



arable companion. Assert nothing that cannot 

 be proved in some simple and decisive fashion. 



"Cultivate the critical spirit. Taken by it- 

 self, it is neither an awakener of ideas nor an 

 incentive to great deeds. But without it noth- 

 ing is stable. It always has the last word. This 

 which I ask of you, and which you in turn will 

 ask of the disciples whom you train, is the thing 

 which of all others is most difficult for an in- 

 ventor. 



"To believe that you have discovered an im- 

 portant scientific fact, to feel a feverish desire 

 to proclaim it, and yet to force yourself, for 

 days and weeks, sometimes for years, to combat 

 your own discovery, to do your utmost to dis- 

 prove your own experiments, and to refrain 

 from announcing what you have discovered un- 

 til you have exhausted every contrary hypothe- 

 sis, that indeed is an arduous task. 



"But when, after all these efforts, you arrive 

 at certainty, you experience one of the greatest 

 joys that the human soul can know, and the 

 thought that you will contribute ,to the honour 



