8 REPORT—1896. 
Pasteur’s acuteness as an observer and his ingenuity in experiment, as 
well as his almost intuitive perception of truth. 
A series of other beautiful investigations followed, clearly proving that 
all true fermentations, including putrefaction, are caused by the growth 
of micro-organisms. 
It was natural that Pasteur should desire to know how the microbes 
which he showed to be the essential causes of the various fermentations 
took their origin. It was at that period a prevalent notion, even among 
many eminent naturalists, that such humble and minute beings originated 
de novo in decomposing organic substances ; the doctrine of spontaneous 
generation, which had been chased successively from various positions 
which it once occupied among creatures visible to the naked eye, having 
taken its last refuge where the objects of study were of such minuteness 
that their habits and history were correspondingly difficult to trace. 
Here again Pasteur at once saw, as if by instinct, on which side the truth 
lay ; and, perceiving its immense importance, he threw himself with ardour 
into its demonstration. J may describe briefly one class of experiments 
which he performed with this object. He charged a series of narrow- 
necked glass flasks with a decoction of yeast, a liquid peculiarly liable to 
alteration on exposure to the air. Having boiled the liquid in each flask, 
to kill any living germs it might contain, he sealed its neck with a blow- 
pipe during ebullition ; after which, the flask being allowed to cool, the 
steam within it condensed, leaving a vacuum above the liquid. If, then, 
the neck of the flask were broken in any locality, the air at that particular 
place would rush in to fill the vacuum, carrying with it any living microbes 
that might be floating in it. The neck of the flask having been again 
sealed, any germs so introduced would in due time manifest their presence 
by developing in the clear liquid. When any of such a series of flasks 
were opened and re-sealed in an inhabited room, or under the trees of a 
forest, multitudes of minute living forms made their appearance in them ; 
but if this was done in a cellar long unused, where the suspended 
organisms, like other dust, might be expected to have all fallen to the 
ground, the decoction remained perfectly clear and unaltered. The oxygen 
and other gaseous constituents of the atmosphere were thus shown to be of 
themselves incapable of inducing any organic development in yeast-water. 
Such is a sample of the many well-devised experiments by which he 
carried to most minds the conviction that, as he expressed it, ‘la généra- 
tion spontanée est wne chimére,’ and that the humblest and minutest living 
organisms can only originate by parentage from beings like themselves, 
Pasteur pointed out the enormous importance of these humble 
organisms in the economy of nature. It is by their agency that the dead 
bodies of plants and animals are resolved into simpler compounds fitted 
for assimilation by new living forms. Without their aid the world would 
be, as Pasteur said, encombré de cadavres. They are essential not only 
to our well-being, but to our very existence. Similar microbes must 
