216 THE HISTORY OF SCIENCE 



rector of the academic, and three years later became 

 Professor of Chemistry. In 1854 he was appointed 

 Dean of the Faculty of Sciences at Lille, a town 

 then officially described as the richest center of in- 

 dustrial activity in the north of France. In his open- 

 ing address he showed the value and attractiveness 

 of practical studies. He believed as an educator in 

 the close alliance of laboratory and factory. Appli- 

 cation should always be the aim, but resting on the 

 severe and solid basis of scientific principles ; for it 

 is theory alone which can bring forth and develop 

 the spirit of invention. 



His own study of racemic acid, begun in the labo- 

 ratories of Paris, and followed up in the factories of 

 Leipzig, Prag, and Vienna, had led to his theory of 

 molecular dissymmetry, the starting point of modern 

 stereo-chemistry. It now gave rise on Pasteur's part 

 to new studies and to new applications to the indus- 

 tries. He tried an experiment which seems almost 

 whimsical, placing ammonium racemate in the ordi- 

 nary conditions of fermentation, and observed that 

 only one part the dextro-rotatory ferments or 

 putrefies. Why ? " Because the ferments of that fer- 

 mentation feed more easily on the right hand than 

 on the left hand molecules." He succeeded in keep- 

 ing alive one of the commonest moulds on the sur- 

 face of ashes and racemic acid, and saw the laevo- 

 tartaric acid appear. It was thus that he passed from 

 the study of crystals to the study of ferments. 



In the middle of the nineteenth century little was 

 known of the nature of fermentation, though some 

 sought to explain by this ill-understood process the 

 origin of various diseases and of putrefaction. Why 



