i 4 INTRODUCTION 



which had escaped even such skilled investigators as 

 Mitscherlich and La Provostaye. Two crystals of pre- 

 cisely the same chemical composition were seen to be 

 identical also in form, except in one respect: although 

 the interfacial angles were the same, the two could not 

 be superposed the small facets were inclined in some 

 cases to the right, and in others to the left. Carefully 

 separated into two heaps and then dissolved, the two 

 types of crystals in solution, though chemically iden- 

 tical, produced opposite effects on a beam of polarized 

 light one rotating it to the right, the other to the left. 

 Mixed in equal parts, they caused no rotation. 



This discovery, to the lay mind so valueless, excited 

 Pasteur beyond measure. He rushed from the laboratory, 

 and in the long alleys of the Luxembourg Gardens 

 unfolded his vision of its consequences to his friend 

 Chappuis. The constitution of racemic acid, formerly 

 so mysterious, had been found; a new class of isomeric 

 substances had been discovered; the phenomenon of 

 rotatory polarization and the properties of crystals had 

 been illuminated: in short, a new and unforeseen route 

 had been opened in science. Biot, when Pasteur repeated 

 the experiment for him, exclaimed: "Mon cher enfant, 

 j'ai tant aime les sciences dans ma vie que cela me fait 

 battre le cceur!" 



Beautiful as this discovery appeared to the veteran 

 Biot, it was still more marvelous in its possibilities to 

 Pasteur himself. For his powerful imagination carried 

 him far beyond its immediate applications in chemistry 

 and physics toward the still greater consequences that 

 he already half divined. Eager to pursue the new path, 

 he followed up his work. How is racemic acid produced? 

 With the aid of Mitscherlich, Pasteur set out in hot 

 haste for the chemical factories of Germany, Austria, and 

 Bohemia. Everywhere he found traces of the acid 



