106 PASTEUR 



ments. On examining the crystals of sodium-ammo- 

 nium salt of racemic acid, he noticed that certain facets 

 giving a degree of asymmetry were always found on 

 the crystals of the optically active salts and acids. On 

 examining the crystals of the racemic acid, he did not 

 find, as he had expected, perfect symmetry ; but he 

 saw that, whilst some of the crystals showed these 

 facets to the right, others showed them to the left. 

 In fact, sodium -ammonium racemate consisted of a 

 mixture of right-handed and left-handed crystals, 

 which neutralized one another as regards the polariza- 

 tion of light, and were thus optically inactive. With 

 infinite patience Pasteur picked out the right from the 

 left handed crystals, and investigated the action of 

 their solutions on polarized light. As he expected, 

 the one sort turned the plane of polarization to the 

 left, the other to the right. A mixture of equal 

 weights of the two kinds of crystals remained optically 

 inactive. ' Tout est trouve !' he exclaimed ; and rush- 

 ing from the laboratory, embraced the first man he 

 came across. ' C'etait un peu comme Archimede,' as 

 his biographer gravely remarks. 



His work immediately attracted attention. Biot, 

 who had devoted a long and strenuous life to the 

 problems of polarization, was at first sceptical, but, 

 after a careful investigation, was convinced. Pasteur 

 began to be talked about in the circle of the Institute. 



In the midst of these researches Pasteur's mother 

 died suddenly, and her son, overwhelmed with grief, 

 remained for weeks almost silent and unable to work. 

 Shortly after this we find the old longing revived, and 

 Pasteur sought at any cost some post near Arbois, 

 somewhere not quite out of the reach of those he 

 loved. Besancon was refused him, but at the begin- 

 ning of 1849 he replaced M. Persoz as Professor of 

 Chemistry at Strasbourg. 



The newly - appointed Rector of the Academy of 



