VIRULENT DISEASES--SPLENIC FEVER, SEPTICÆMIA 176 FOWL CHOLERA 212 ATTENUATED VIRUS, OR VACCINATION-- THE FOWL CHOLERA VACCINE 220 THE VACCINE OF SPLENIC FEVER 231 THE RETURN TO VIRULENCE 246 ETIOLOGY OF SPLENIC FEVER 250 METHOD OF DISCUSSION AND CONTRADICTIONS 262 THE LABORATORY OF THE ÉCOLE NORMALE-- VARIOUS STUDIES--HYDROPHOBIA 271 INTRODUCTION. In the early part of the present year the French original of this work was sent to me from Paris by its author. It was accompanied by a letter from M. Pasteur, expressing his desire to have the work translated and published in England. Responding to this desire, I placed the book in the hands of the Messrs. Longman, who, in the exercise of their own judgment, decided on publication. The translation was confided, at my suggestion, to Lady Claud Hamilton. The translator's task was not always an easy one, but it has, I think, been well executed. A few slight abbreviations, for which I am responsible, have been introduced, but in no case do they affect the sense. It was, moreover, found difficult to render into suitable English the title of the original: '_M. Pasteur, Histoire d'un Savant par un Ignorant_.' A less piquant and antithetical English title was, therefore, substituted for the French one. This filial tribute, for such it is, was written, under the immediate supervision of M. Pasteur, by his devoted and admiring son-in-law, M. Valery Radot. It is the record of a life of extraordinary scientific ardour and success, the picture of a mind on which facts fall like germs upon a nutritive soil, and, like germs so favoured, undergo rapid increase and multiplication. One hardly knows which to admire most--the intuitive vision which discerns in advance the new issues to which existing data point, or the skill in device, the adaptation of means to ends, whereby the intuition is brought to the test and ordeal of experiment.