THE QUESTION OF SPONTANEOUS GENEKATION. 99 



mercury. In these circumstances ebullition goes on 

 under a pressure greater than that of the atmo- 

 sphere, consequently at a temperature higher than 

 100 degrees Centigrade. 



It remained, however, to be proved that the floating 

 dust of the air embraces the germs of the lower 

 organisms. Through a tube stopped with cotton 

 wool, Pasteur, by means of an aspirator, drew ordi- 

 nary air. In passing through the wool it was filtered, 

 depositing therein all its dust. Taking a watch-glass, 

 Pasteur placed on it a drop of water in which he 

 steeped the cotton wool stopper and squeezed out of 

 it, upon a glass slide, a drop of water which contained 

 a portion of the intercepted dust. He repeated this 

 process until he had extracted from the cotton nearly 

 all the intercepted dust. The operation is simple and 

 easily executed. Placing the glass slide with a little of 

 the soiled liquid under a microscope, we can dis- 

 tinguish particles of soot, fragments of silk, scraps of 

 wool, or of cotton. But, in the midst of this inani- 



I mate dust, living particles make their appearance 

 that is to say, organisms belonging to the animal or 



I vegetable kingdom, eggs of infusoria, and spores of 

 cryptogams. Germs, animalculae, flakes of mildew, 

 float in the atmosphere, ready to fall into any appro- 



, priate medium, and to develop themselves at a pro- 



! digious rate* 



But are these apparently organised particles 





