INTRODUCTION 15 



in tartrates. Returning to Paris, he succeeded in pro- 

 ducing racemic acid experimentally, and incidentally 

 won the Chevalier's ribbon of the Legion of Honor. 



Twenty years later, as a direct consequence of these 

 experiments on crystalline dissymmetry, arose the new 

 science of stereochemistry, which tells us of the arrange- 

 ment in space of the atoms constituting a molecule. 

 But far more important, Pasteur's studies of racemic 

 acid showed him that while one class of crystals would 

 ferment, the others remained inert in the liquid. Why 

 should this be? Because, he replied, "Les ferments de 

 cette fermentation se nourrissent plus facilement des 

 molecules droites que des molecules gaudies." But 

 what, then, is fermentation, that strange process regarded 

 by Liebig and others as a purely chemical phenomenon? 

 The answer was immediately given by Pasteur, who 

 showed it to be due to the presence of hosts of bacteria, 

 which eagerly devoured one class of crystals and ignored 

 the others. 



Here was the beginning of that great study of putre- 

 factive changes, and of the part played by bacteria in 

 disease, which made the world Pasteur's debtor. 

 Modern surgery, the cure of rabies, the germ theory of 

 infection, all go back to those simple experiments 

 in pure science that laid the foundation of his career. 

 What a privilege for the student to follow in his foot- 

 steps, to feel the stimulus of his example, to realize in 

 some measure that high sense of devotion to truth, 

 of obligation to humanity, best typified in Louis Pasteur! 



But the fascination of Pasteur has tempted us far 

 afield. Here in the Luxembourg Gardens, to which 

 his talks with Chappuis have brought us back, we may 

 well pause to reflect on the demands that the American 

 student may fairly make on the country he elects for 



