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The sentence in his Lille speech, " in the fields of observa- 

 tion, chance only favours the mind which is prepared," was 

 particularly applicable to him. In the summer of 1856 a 

 Lille manufacturer, M. Bigb, had, like many others that same 

 year, met with great disappointments in the manufacture of 

 beetroot alcohol. He came to the young Dean for advice. 

 The prospect of doing a kindness, of communicating the results 

 of his observations to the numerous hearers who crowded the 

 small theatre of the Faculty, and of closely studying the pheno- 

 mena of fermentation which preoccupied him to such a degree, 

 caused Pasteur to consent to make some experiments. He 

 spent some time almost daily at the factory. On his return 

 to his laboratory where he only had a student's microscope 

 and a most primitive coke-fed stove he examined the globules 

 in the fermentation juice, he compared filtered with non- 

 filtered beetroot juice, and conceived stimulating hypotheses 

 often to be abandoned in face of a fact in contradiction with 

 them. Above some note made a few days previously, where 

 a suggested hypothesis had not been verified by fact, he would 

 write: "error," "erroneous," for he was implacable in his 

 criticism of himself. 



M. Bigo's son, who studied in Pasteur's laboratory, has 

 summed up in a letter how these accidents of manufacture 

 became a starting point to Pasteur's investigations on fer- 

 mentation, particularly alcoholic fermentation. "Pasteur 

 had noticed through the microscope that the globules were 

 round when fermentation was healthy, that they lengthened 

 when alteration began, and were quite long when fermen- 

 tation became lactic. This very simple method allowed us 

 to watch the process and to avoid the failures in fermentation 

 which we used so often to meet with. ... I had the good 

 fortune to be many times the confidant of the enthusiasms 

 and disappointments of a great man of science." Young 

 Bigo indeed remembered the series of experiments, the 

 numerous observations noted, and how Pasteur, whilst study- 

 ing the causes of those failures in the distillery, had wondered 

 whether he was not confronted with a general fact, common 

 to all fermentations. Pasteur was on the road to a discovery 

 the consequences of which were to revolutionize chemistry. 

 During months and months he worked to assure himself that 

 he was not a prey to error. 



In order to appreciate the importance of the ideas which 



