102 PASTEUR: THE HISTORY OF A MIND 



Lussac had seen some inert must of grape begin to fer- 

 ment as soon as he placed it in contact with some bubbles 

 of external air. Men had concluded from this, with 

 some appearance of justice, that there was in each bubble 

 of air something capable of starting all the fermentations 

 or putrefactions which could take place in the most varied 

 liquids in contact with air. This was, it is true, a little 

 too liberal an interpretation given to an experiment which 

 had been performed only twice and had succeeded only 

 once. But if it accorded well with the hypothesis of 

 spontaneous generation which saw in the oxygen the 

 only cause of the appearance of life, it could not accom- 

 modate itself to the theory of germs. It seemed difficult 

 that there should be sufficient in each bubble of air to 

 populate the most varied liquids with the most varied 

 microbes. 



What degree of credence and of generality could be 

 attributed to the experiment of Gay-Lussac? This was 

 what no one knew, and what Pasteur was obliged to 

 study. It is this part of his work which has attracted 

 the most attention, not that it is the best: all of it is 

 valuable; but this is the most easily understood, and the 

 experiments in it are as simple as they are convincing. 

 Pasteur took again his flasks with a straight neck drawn 

 out. He brought to a boil the organic infusion which 

 they contained, and after having driven out all the air 

 from the interior, through the open extremity of the neck, 

 he closed this at the moment when the steam was given 

 off by melting the glass in the flame of a blowpipe. The 

 flask is thus practically empty of air when it is cooled. 



He then took 20 or 40 of these flasks to the place where 

 he wished to make a study of the air, and broke the necks 

 with a long pair of pincers, having first taken the precau- 

 tion to pass the necks and the pincers through the flame 

 of an alcohol lamp, in order to kill all the germs which 



