POUCHET, PASTEUR: THE GERMS OF THE AIR 93 



ferment upon the entrance of some bubbles of air. You 

 say these bubbles brought with them some germs of 

 yeast, but they brought something else into an infusion 

 of hay, and still other germs into a meat infusion, etc. 

 That makes a great many germs!" And Pouchet, who 

 was a man of imagination, added: "The air thus peopled 

 would have the density or iron." 



To all these reasons for doubt, add this one, to which 

 we have referred above, and which was more profound 

 and more powerful, being more general, namely that, in 

 the phenomena of spontaneous generation, even more 

 than in fermentations, chance seemed to be master and 

 to dictate according to its caprice the kinds of population 

 of the infusions, and of destruction of their elements. 

 Spontaneous fermentations, spontaneous generations, 

 chance, all these words harmonized well and entered 

 en bloc the minds of the scientific men. 



It is here that we again recur to Pasteur, and to that 

 quality of which I have just spoken the superiority of 

 his equipment for entering the fray. The idea of speci- 

 ficity, born of his work on the fermentations, involved 

 that of hereditary characters, which in its turn led to that 

 of an ordinary kind of generation. Pasteur inclined, 

 therefore, logically toward the theory of germs. It was 

 only a question of proving it by experimentation, and for 

 that he was better equipped than any scientific man of 

 his time. He was familiar with the infinitely small 

 organisms; he knew how to manipulate them. He had 

 a clear field: and he advanced with great strides. 



"You pretend," he said to the partisans of spontaneous 

 generation, "that there are not enough living germs in 

 the air to explain the fertility of the infusions with which 

 this air comes in contact: what do you know about it? 

 You have examined the dust deposited on furniture and 

 on stones; you have gone to investigate it in the aban- 



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