ORIGIN OF LOWEST ORGANISMS. 35 



the textile fabrics and of the organic products of 

 various kinds which are daily subservient to the wants 

 of rnan ; and that the chimneys of manufactories and 

 dwelling-houses are also continually emitting clouds 

 of smoke thick with imperfectly consumed organic 

 particles, some idea may be gained of the manifold 

 sources whence the organic particles and fragments 

 found in the atmosphere may emanate, and also as to 

 what proportion of them is likely to be composed of 

 living or dead reproductive elements, or " germs." 



Thus, then, so far as the two rival doctrines of fer- 

 mentation are concerned, the investigation of the 

 nature of the solid particles contained in the atmo- 

 sphere has revealed facts which are thoroughly in. 

 harmony with all the requirements of Liebig's phy- 

 sical theory, though it has almost utterly failed to give 

 anything like a scientific basis to the vital theory of 

 Pasteur. So far from being able to show that living 

 Bacteria (which are the first and oftentimes the only 

 organisms concerned in many processes of fermenta- 

 tion and putrefaction) are universally diffused through 

 the air, Pasteur admits that these cannot be detected, 

 and that their " germs " are not recognizable. 



If, therefore, M. Pasteur still maintains the truth of 

 his theory, it should be distinctly understood that it 

 rests originally, not upon established facts, but upon 

 a mere hypothesis the hypothesis that the air teems 

 with multitudes of invisible Bacteria germs. He is 

 driven to such a doctrine, not only by his own con- 



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