INTRODUCTION. xxi 



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 

 abandonment of which he still regrets. A German 

 manufacturer of chemicals had noticed that the im- 

 pure commercial 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 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 



soda produces circular polarisation in all directions 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. 



