78 ORIGINATION OF LIVING BEINGS. 



yeast, or perhaps some other artificial preparation, and 

 filled a vessel having a long tubular neck, with it. He 

 then boiled the liquid and bent that long neck into an 

 S shape or zig-zag, leaving it open at the end. The 

 infusion then gave no trace of any appearance of spon- 

 taneous generation, however long it might be left, as 

 all the germs in the air were deposited in the beginning 

 of the bent neck. He then cut the tube close to the 

 vessel, and allowed the ordinary air to have free and 

 direct access ; and the result of that was the appearance 

 of organisms in it, as soon as the infusion had been 

 allowed to stand long enough to allow of the growth 

 of those it received from the air, which was about forty- 

 eight hours. The result of M. Pasteur's experiments 

 proved, therefore, in the most conclusive manner, that all 

 the appearances of spontaneous generation arose from 

 nothing more than the deposition of the germs of or- 

 ganisms which were constantly floating in the air. 



To this conclusion, however, the objection was 

 made, that if that were the cause, then the air would 

 contain such an enormous number of these germs, that 

 it would be a continual fog. But M. Pasteur replied 

 that they are not there in anything like the number we 

 might suppose, and that an exaggerated view has been 

 held on that subject ; he showed that the chances of 

 animal or vegetable life appearing in infusions, depend 

 entirely on the conditions under which they are ex- 

 posed. If they are exposed to the ordinary atmosphere 

 around us, why, of course, you may have organisms 

 appearing early. But, on the other hand, if they are 

 exposed to air from a great height, or from some very 

 quiet cellar, you will often not find a single trace of 

 life. 



