X INTRODUCTION 



problems of biology, and it placed his name high in the group 

 of the most illustrious benefactors of practical industries. 



The national tragedy of 1870-2 nearly killed Pasteur. He 

 had a terrible pilgrimage to make in search of his son, a 

 sergeant in Bourbaki's force. *'The retreat from Moscow 

 cannot have been worse than this,'' said the savant. In 

 October, 1868, he had had a stroke of paralysis, from which 

 he recovered in a most exceptional way, as it seemed to have 

 diminished neither his enthusiasm nor his energy. In a series 

 of studies on the diseases of beer, and on the mode of production 

 of vinegar, he became more and more convinced that these 

 studies on fermentation had given him the key to the nature of 

 the infectious diseases. It is a remarkable fact that the distin- 

 guished EnglisJi philosopher of the seventeenth century, the 

 •rnan who more than any one else of his century appreciated the 

 importance of the experimental method, Robert Boyle, had 

 said that he who could discover the nature of ferments and 

 fermentation, would be more capable than anyone else of 

 explaining the nature of certain diseases. The studies on 

 spontaneous generation, and Lister's application of the germ 

 theory to the treatment of wounds, had aroused the greatest 

 interest in the medical world, and Villemin, in a series of most 

 brilliant experiments, had demonstrated the infectivity of 

 tuberculosis. An extraordinary opportunity now offered for the 

 study of a widespread epidemic disease, known as anthrax, 

 which in many parts of France killed from 25 to 30 per cent, of 

 the sheep and cattle, and which in parts of Europe had been 

 pandemic, attacking both man and beast. As far back as 1838 

 minute rods had been noted in the blood of animals which had 

 died from the disease ; and in 1863 Devaine thought that these 

 little bodies, which he called bacteridia, were the cause of the 

 disease. In 1876 a young German district physician, Robert 

 Koch, began a career, which in interest and importance rivals 

 that of the subject of this memoir. Koch confirmed in every 

 point the old researches of Devaine; but he did much more, 

 and for the first time isolated the organism in pure culture 

 outside the body, grew successive generations, showed the 



