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process of decay, as the quotation from Liebig already given 
shows. Physiologists and microscopists have been more 
inclined to consider it as an organised substance. When 
Gay Lussac passed a bubble of air into the juice of grapes, 
and found that fermentation began at once, it was believed 
that the oxygen was the prime mover, and that, when once 
begun, the action did not cease. When, however, Dusch 
and Schroeder found that flesh did not decompose if the 
air was previously passed through a good filter of cotton 
wool, some difficulty was thrown on the subject. It would 
appear as if oxygen were not the only agent in the 
atmosphere causing decomposition. The investigations of 
M. Pasteur, who found the subject in this uncertain con- 
dition, have advanced it so far that we may now with 
certainty reason in the belief that organized substances are 
really found in great abundance in the atmosphere (in all 
places), and that they are the cause of some hitherto entirely 
mysterious phenomena, putrefaction included. His object 
was first to inquire into the possibility of spontaneous genera- 
tion, and he found that carefully filtered air allowed no 
organisms to appear in vegetable solutions, He found that 
near the usual surface of the ground these organisms were 
so numerous that whenever a vessel containing vegetable 
matter fit for their growth was opened for a very short 
time they were found to enter, that in cellars and damp and 
quiet places, where there was no air or dust floating about, 
these organisms were fewer, and that, as he ascended the 
sides of the Alps and the Jura, they diminished in number. 
A commission of the French Academy confirmed his results. 
If *we examine previous enquiries into the compounds 
resulting from the decomposition of organic substances, 
we shall find nothing which is at all calculated to bring out 
such an intelligible rational view of the origin of many 
diseases, and also of some phases of putrefaction. Chemists, 
when they have examined products of the latter action 
