Septebibee 25, 1896.] 



SCIENCE. 



413 



animal substance, such as fibrin, to a solution 

 of sugar, together with chalk that should 

 combine with the acid as it was formed. 

 Pasteur saw, what had never before been 

 noticed, that a fine gray deposit was formed, 

 differing little in appearance from the de- 

 composing fibrin, but steadily increasing as 

 the fermentation proceeded. Struck by the 

 analogy presented by the increasing deposit 

 to the growth of yeast in sweetwort, he ex- 

 amined it with the microscope, and found 

 it to consist of minute particles of uniform 

 size. Pasteur was not a biologist, but al- 

 though these particles were of extreme 

 minuteness in comparison with the constit- 

 uents of the yeast plant, he felt convinced 

 that they were of an analogous nature, the 

 cells of a tiny microscopic fungus. This he 

 regarded as the essential ferment, the fibrin 

 or other so-called ferment serving, as he be- 

 lieved, merely the purpose of supplying to 

 the growing plant certain chemical ingredi- 

 ents not contained in the sugar, but essen- 

 tial to its nutrition. And the correctness 

 of this view he confirmed in a very striking 

 manner, by doing away with the fibrin or 

 other animal material altogether, and sub- 

 stituting for it mineral salts containing the 

 requisite chemical elements. A trace of 

 the gray deposit being applied to a solution 

 of sugar containing these salts, in addition 

 to the chalk, a brisker lactic fermentation 

 ensued than could be procured in the ordi- 

 nary way. 



I have referred to this research in some 

 detail because it illustrates Pasteur's acute- 

 ness as an observer and his ingenuity in ex- 

 periment, as well as his almost intuitive 

 perception of truth. 



A series of other beautiful investigations 

 followed, clearly proving that all true fer- 

 mentations, including putrefaction, are 

 caused by the growth of micro-organisms. 



It was natural that Pasteur should de- 

 sire 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 successivelj'" from 

 various positions which it once occupied 

 among creatures visible to the naked eye, 

 having taken its last refuge where the ob- 

 jects of study were of such minuteness that 

 their habits and history were correspond- 

 ingly difiicult 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. I 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. Hav- 

 ing boiled the liquid in each flask, to kill 

 any living germs it might contain, he 

 sealed its neck with a blowpipe during 

 ebullition ; after which the flask being al- 

 lowed to cool, the stream within it con- 

 densed, 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, multi- 

 tudes of minute living forms made their ap- 

 pearance in them ; but if this was done in 

 a cellar long unused, where the suspended 

 organisms, like other dust, might be ex- 

 pected to have all fallen to the ground, the 

 decoction remained perfectly clear and un- 

 altered. The oxygen and other gaseous 



