PASTEUR'S RESEARCHES IN GERM-LIFE. 8 7 



mercial tartrate of lime, sullied with organic matters of various kinds, 

 fermented on being dissolved in water and exposed to summer heat. 

 Thus prompted, Pasteur prepared some pure, right-handed tartrate of 

 ammonia, mixed with it albuminous matter, and found that the mixt- 

 ure fermented. His solution, limpid at first, became turbid, and the 

 turbidity he found to be due to the multiplication of a microscopic or- 

 ganism, which found in the liquid its proper aliment. Pasteur recog- 

 nized in this little organism a living ferment. This bold conclusion 

 was doubtless strengthened, if not pi - ompted, by the previous dis- 

 covery of the yeast-plant the alcoholic ferment by Cagniard-Latour 

 and Schwann. 



Pasteur next permitted his little organism to take the carbon neces- 

 sary for its growth from the pure paratartrate of ammonia. Owing 

 to the opposition of its two classes of crystals, a solution of this salt, 

 it will be remembered, does not turn the plane of polarized light either 

 to the right or to the left. Soon after fermentation had set in, a rota- 

 tion to the left was noticed, proving that the equilibrium previously 

 existing between the two classes of crystals had ceased. The rotation 

 reached a maximum, after which it was found that all the right-handed 

 tartrate had disappeared from the liquid. The organism thus proved 

 itself competent to select its own food. It found, as it were, one of 

 the tartrates more digestible than the other, and appropriated it, to the 

 neglect of the other. No difference of chemical constitution deter- 

 mined its choice ; for the elements, and the proportions of the ele- 

 ments, in the two tartrates were identical. But the peculiarity of 

 structure which enabled the substance to rotate the plane of polariza- 

 tion to the right also rendered it a fit aliment for the organism. This 

 most remarkable experiment was successfully made with the seeds of 

 our common mold {Penicillium glaucum). 



Here we find Pasteur unexpectedly landed amid the phenomena of 

 fermentation. With true scientific instinct he closed with the concep- 

 tion that ferments are, in all cases, living things, and that the sub- 

 stances formerly regarded as ferments are in reality the food of the 

 ferments. Touched by this wand, difficulties fell rapidly before him. 

 He proved the ferment of lactic acid to be an organism of a certain 

 kind. The ferment of butyric acid he proved to be an organism of a 

 different kind. He was soon led to the fundamental conclusion that 

 the capacity of an organism to act as a ferment depended on its 

 power to live without air. The fermentation of beer was sufficient to 

 suggest this idea. The yeast-plant, like many others, can live either 

 with or without free air. It flourishes best in contact with free air, 

 for it is then spared the labor of wresting from the malt the oxygen 

 required for its sustenance. Supplied with free air, however," it 

 practically ceases to be a ferment ; while in the brewing-vat, where 

 the work of fermentation is active, the budding torula is completely 

 cut off by the sides of the vessel, and by a deep layer of carbonic-acid 



