PASTEUR 3 



that the property of optical activity, possessed by certain organic compoundB 

 was characteristic of substances synthesized by living things, as contrasted with 

 substances synthesized in the laboratory. It was known that small amounts of 

 an optically active substance, amyl alcohol, were formed during the fermentation 

 of sugar, especially in association with the lactic fermentation. Since it was 

 impossible to regard the molecule of amyl alcohol as derived from the molecule 

 of sugar by any simple break-down process, he was led to the conclusion that 

 the optically active molecule of the sugar was first broken down to relatively 

 simple substances, which experience had shown to be without optical activity, 



Fig. 1.— Louis Pasteur (1822-1895). 



and that from such inactive substances the optically active amyl alcohol was 

 synthesized. For Pasteur this was evidence of the presence and activity of 

 living things, and he therefore started on his study of fermentation with a strong 

 a priori leaning towards the microbial theory of fermentation, and away from 

 the then dominant hypothesis of Liebig. He was prepared to adopt the 

 theories already propounded by Cagniard-Latour in 1836, and by Schwann 

 in 1837, concerning the living nature of the yeast globules, which were always 

 to be found in sugar solutions undergoing alcoholic fermentations, and which 

 had been described by van Leeuwenhoek in 1680. 



Since, however, it was in the lactic fermentation that the production of amyl 



