34 ORIGIN OF LOWEST ORGANISMS. 



way of inference, than the assumption at once indulged 

 in by Prof. Tyndall and others (who might have been 

 expected, by their previous scientific work, to have 

 learned more caution) that this impalpable organic dust 

 was largely composed of impalpable germs. Yet, with- 

 out a shadow of proof, without even an attempt to 

 prove it, the air was for a time represented to be a 

 mere stirabout, thick with invisible germs. The 

 briefest reflection, however, upon the probabilities of 

 the case, should have sufficed to suggest a totally dif- 

 ferent interpretation. The surface of the earth is 

 clothed with living things of all kinds, animal and 

 vegetal, which are not only continually throwing off 

 organic particles and fragments during their life, but 

 are constantly undergoing processes of decay and mole- 

 cular disintegration after their death. The actual re- 

 productive elements of these living things are ex- 

 tremely small in bulk, when compared with the other 

 parts which are not reproductive, and although Bacteria 

 and Torulce&Q exist abundantly, and do materially help 

 to bring about some of the decay in question, yet their 

 bulk, also, is extremely small in comparison with the 

 amount of organic matter itself that is continually 

 undergoing disintegration of a dry kind, in which 

 Bacteria and Torulce take no part. When, moreover, 

 it is considered that in the neighbourhood of populous 

 cities (the air of which alone exhibits this very large 

 quantity of impalpable, mixed with palpable, organic 

 dust), there is constantly going on a wear and tear of 



