NATURAL SCIENCE IN THE NINETEENTH CENTURY 379 



studied by several workers of eminence among whom was 

 Helmholtz but it was chiefly Pasteur who in a memorable series 

 of researches finally proved that yeast is the one and only cause 

 of the alcoholic fermentation, a biological or " germ " theory 

 of fermentation, thus displacing Liebig's chemical or catalytic 

 theory, the germ in this case being yeast. By the use of the 

 microscope, combined with new and ingenious methods of culti- 

 vation of yeast and other microbes, Pasteur, between 1859 

 and 1865, proved beyond doubt that yeast is the agent of the 

 alcoholic fermentation and that other microbes are the agents of 

 other familiar fermentations, such as the butyric and acetic. His 

 work was marked by remarkable precision and refinement. 



From a germ theory of normal fermentations, putrefactions, 

 and decay it was a short step to a germ theory of undesirable or 

 abnormal fermentations, such as often occur in brewing and wine 

 making. In these last, the microscope revealed to Pasteur the 

 presence of strange forms foreign to the ordinary fermentation, 

 and evidently wild yeast, moulds, or other extraneous microbes 

 which by interfering with or supplanting the normal forms, pro- 

 duced disagreeable, or abnormal, i.e. "diseased", beer or wine. 



Similarly, it was only a second step from the diseases of wine 

 and beer to those of animals and man. A disastrous epidemic 

 disease affecting silkworms in the south of France at this time 

 brought to Pasteur an urgent request that he should make an 

 investigation. "But," said Pasteur, "I have never handled a 

 silkworm." "So much the better," said Dumas, the chemist, who 

 insisted that he should thus patriotically enter the field of animal 

 pathology. Pasteur yielded and spent three years in studies upon 

 the silkworm disease, with results invaluable to science and espe- 

 cially to pathology. 



ANTISEPTIC AND ASEPTIC SURGERY. LISTER. Meantime 

 Lister, an English surgeon resident in Edinburgh, led on by 

 Pasteur's researches, introduced a new and scientific treatment of 

 open wounds, based on the germ theory. Open wounds whether 

 made by accident or in surgery ordinarily suppurate, i.e. become 

 red, swollen and inflamed and eventually produce pus. Lister 



