98 PASTEUR I THE HISTORY OF A MIND 



Pasteur did not stop midway. "Do you pretend," he 

 continued, addressing the partisans of spontaneous 

 generation, "that the cotton, as such, plays some part 

 in the phenomenon? Never mind! We will replace it 

 with calcined amianthus, without in any way changing 

 the result. You pretend that the cotton would have 

 absorbed, by contact with the air which has traversed 

 it, some vapor, or I know not what subtile matter which 

 heat can destroy, and which, entering the infusion with 

 the cotton, would have brought there one of the condi- 

 tions necessary for life. Your hypothesis is somewhat 

 intangible. But there is nothing more mysterious than 

 life itself, and I will reply to it. 



"After having introduced into the flask an infusion 

 capable of fermentation, draw out the neck in an enamel- 

 ler's lamp, in such a way as to make a bent and sinuous 

 tube, in the form of a letter S (Fig. 12). Then boil the 

 liquid. When vapor has issued from the orifice of the 

 neck for some minutes, drawing out all the air of the 

 flask with it, extinguish the flame and let the flask cool. 

 The flask becomes filled with ordinary air which will not 

 have been heated, and which will enter it with all its 

 elements, both known and unknown. As the neck 

 remains open, diffusion will produce incessant exchanges 

 between the air of the flask and the atmosphere outside. 

 Nevertheless, the flask remains indefinitely sterile. How 

 do you explain this result, you partisans of spontaneous 

 generation? There you have organic matter, water, air 

 incessantly renewed, and heat, nevertheless nothing 

 appears in the liquid. You will say that the genetic power 

 of the infusion has been altered by the boiling to which 

 we have subjected it. But if, without touching the 

 infusion, I cut off the neck of the flask which contains 

 it, in such a way as to leave it exposed to the fall of 

 atmospheric dust, it becomes clouded in two or three 



