182 LOUIS PASTEUR, 



Theory, however, may change, and inference may 

 fade away, but scientific experiment endures for ever. 

 Such durability belongs, in the domain of molecular 

 physics, to the experimental researches of M. Pasteur. 



The weightiest events of life sometimes turn upon 

 small hinges; and we now come to the incident which 

 caused M. Pasteur to quit a line of research the abandon- 

 ment of which he still regrets. A German manu- 

 facturer of chemicals had noticed that the impure com- 

 mercial tartrate of lime, sullied with organic matters 

 of various kinds, fermented when it was 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 mixture fermented. His solution, limpid at 

 first, became turbid, and the turbidity he found to be 

 due to the multiplication of a microscopic organism, 

 which found in the liquid its proper aliment. Pasteur 

 recognised in this little organism a living ferment. 

 This bold conclusion was doubtless strengthened, if 

 not prompted, by the previous discovery of the yeast- 

 plant the alcoholic ferment by Cagniard-Latour and 

 Schwann. 



Pasteur next permitted his little organism to take 

 the carbon necessary 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 polarised 

 light either to the right or to the left. Soon after 

 fermentation had set in, a rotation to the left was 

 noticed, proving that the equilibrium previously exist- 



tions through the crystal, while in quartz it occurs only in the 

 direction of the^axis. Marbach also discovered facets upon his 

 crystals, resembling those of quartz. 



