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heterogenia or spontaneous generation Joly and Musset agreed 

 in affirming that " they did not mean a creation out of nothing, 

 but the production of a new organized being, lacking parents, 

 and of which the primordial elements are drawn from ambient 

 organic matter." 



Thus supported, Pouchet multiplied objections to the views 

 of Pasteur, who had to meet every argument. Pasteur in- 

 tended to narrow more and more the sphere of discussion. It 

 was an ingenious operation to take the dusts from a cotton-wool 

 filter, to disseminate them in a liquid, and thus to determine 

 the alteration of that liquid ; but the cotton wool itself was an 

 organic substance and might be suspected. He therefore sub- 

 stituted for the cotton wool a plug of asbestos fibre, a mineral 

 substance. He invented little glass flasks with a long curved 

 neck ; he filled them with an alterable liquid, which he de- 

 prived of germs by ebullition ; the flask was in communication 

 with the outer air through its curved tube, but the atmospheric 

 germs were deposited in the curve of the neck without reaching 

 the liquid ; in order that alteration should take place, the vessel 

 had to be inclined until the point where the liquid reached the 

 dusts in the neck. 



But Pouchet said, " How could germs contained in the air 

 be numerous enough to develop in every organic infusion? 

 Such a crowd of them would produce a thick mist as dense as 

 iron." Of all the difficulties this last seemed to Pasteur the 

 hardest to solve. Could it not be that the dissemination of 

 germs was more or less thick according to places? " Then," 

 cried the heterogenists , ' ' there would be sterile zones and 

 fecund zones, a most convenient hypothesis, indeed ! " Pasteur 

 let them laugh whilst he was preparing a series of flasks re- 

 served for divers experiments. If spontaneous generation 

 existed , it should invariably occur in vessels filled with the same 

 alterable liquid. " Yet it is ever possible," affirmed Pasteur, 

 ' ' to take up in certain places a notable though limited volume 

 of ordinary air, having been submitted to no physical or 

 chemical change, and still absolutely incapable of producing any 

 alteration in an eminently putrescible liquor." He was ready 

 to prove that nothing was easier than to increase or to reduce 

 the number either of the vessels where productions should ap- 

 pear or of the vessels where those productions should be lacking. 

 After introducing into a series of flasks of a capacity of 250 

 cubic centimetres a very easily corrupted liquid, such as yeast 



