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SCIENCE. 



[N. S. Vol. II. No. 45. 



ference which started Pasteur along the line 

 of his experiments in fermentation. It was 

 the guiding star of Pasteur's life. From 

 the moment the inference was drawn until 

 his death this law, that fermentations, putre- 

 factions and all similar chemical changes 

 were produced by the growth of micro- 

 organisms, was the basis of every line of in- 

 vestigation which was undertaken by him. 

 Everjr new problem in his life was attacked 

 by him from this standpoint. The great 

 success of Pasteur's work lay in the fact 

 that his guiding principle was a correct 

 one, his great merit in his wisdom in early 

 adopting it as a law, and his genius in 

 demonstrating it. If he had drawn an in- 

 accurate conclusion from these early ex- 

 periments he might in time have corrected 

 the error, but we must look upon the fact 

 that he had the wisdom to draw a correct 

 inference from this first work as the founda- 

 tion of Pasteur's success in life. 



Pasteur now became interested in the 

 subject of fermentation. His home was in 

 one of the important seats of fermentative 

 industries, and study of fermentation as a 

 general phenomena at once received his at- 

 tention, not only from its general interest, 

 but as especiallj' appropriate to his life at 

 LiUe. He Avas thus led away from the line 

 of pure chemistry iuto biological work, but 

 the change was almost imperceptible. Up 

 to the time when Pasteur began his studies 

 fermentation had been regarded as a chem- 

 ical phenomenon, and it was natural that a 

 chemist should study it. In the few dec- 

 ades that preceded the work of Pasteur, 

 fermentation had been carefully studied by 

 a number of our chemists and microscop- 

 ists. While different theories had been ad- 

 vanced, the theory of fermentation, which 

 was almost universally held at the time 

 when Pasteur began his experiments, was 

 that of the chemist Liebig and was a 

 purely chemical theorj'. In accordance 

 with this theory of Liebig, fermentation is 



simply the chemical decomposition of bodies 

 produced by the unstable equilibrium of 

 their molecules. This theory held that the 

 molecules of fermentable materials were 

 very unstable and were easily broken to 

 pieces into simpler compounds. The fer- 

 ment was held to be simply an exciting cause 

 which started this chemical decomposition. 

 Fermentation was thus a purely chemical 

 subject at the time when Pasteur began his 

 studies, and the first work which he at- 

 tempted was to show that the chemical 

 theory of the scientists of his day should 

 be replaced by the physiological or biological 

 theory which he was convinced from his 

 experiments was the correct one. Upon 

 this task he set himself at once, and by the 

 study of the lactic fermentation of milk, 

 the butyric fermentation of milk, the acetic 

 acid fermentation in the manufactm-e of 

 vinegar, and by the numerous careful ex- 

 periments along these various lines which 

 he devised in his laboratory, it required only 

 four or five years for him to undermine 

 completely the chemical theory of Liebig 

 and to put in its place, on a somewhat un- 

 stable basis at first, perhaps, the theory 

 that all types of fermentation are organic 

 in their nature and produced by the Ufe of 

 microscopic organisms. Even at this early 

 day we can see his recognition of the value 

 of the practical application of science, for 

 among the very early pieces of work which 

 he performed was the study of the acetic 

 acid fermentation in the making of vinegar, 

 and by a practical application of his results 

 to this industry he developed a vast im- 

 provement in the manufacture of vinegar 

 and a great cheapening of the process. 



Pasteur had thus made something his own, 

 and at this date, in the vicinity of 1860, he 

 became recognized as the exponent of the 

 biological theory of fermentation. From 

 this time he progressed rapidly. The fer- 

 mentation of wine next claimed his atten- 

 tion . Here was a second fermentative indus- 



