'The accounts which I have read,' Pasteur remarked some months ago, 'of the spontaneous appearance of the plague in Benghazi in 1856 and in 1858 tend to prove that this outbreak could not be traced to any original contagion. Let us suppose, guided by the facts now known to us, that the plague, a malignant disease belonging to certain countries, has germs of long duration. In all these countries its attenuated virus must exist, ready to resume its active form whenever the conditions of climate, of famine, of misery present themselves afresh. The condition of long duration in the vitality of the germs of evil is not even indispensable; for, if I may believe the doctors who have visited these countries, in all places subject to the plague, and in the intervals of the great outbreaks of the epidemic, cases may be met with of people attacked with boils, not fatal, but resembling those of the deadly plague. Is it not probable that these boils contain an attenuated virus of the plague, and that the passage of this virus into exhausted bodies, which abound only too freely in periods of famine, may restore to it a greater virulence? 'The same may be the case with other maladies which appear suddenly, like typhus in armies and in camps. Without doubt, the germs which are the authors of these diseases are everywhere scattered around, but attenuated; and in this state a man may carry them about him or in his intestinal canal without great damage. They only become dangerous when, by conditions of overcrowding, and perhaps of successive developments on the surfaces of wounds, in bodies enfeebled by disease, their virulence is reinforced.' _ETIOLOGY OF SPLENIC FEVER._ M. Pasteur had triumphed over splenic fever with as much rigour as precision. But he considered that he had still to make one further investigation. He had established the effects of the pest; he had discovered a preventive method with which to combat it: he now wished to know the origin of the evil. Whence comes splenic fever? Why is it endemic in certain departments of France, in certain parts of Russia, Germany, Austria, Italy, Spain, and America? How is it sustained? It was for a long time believed that splenic fever was born spontaneously under the influence of various accidental causes. M. Bouley has related, in his learned work on the 'Progress of Medicine by Experimentation,' that in 1842 the Minister of Agriculture, M. Cunin-Gridaine, at the request of the deputies of the departments that were ravaged by the epidemic, entrusted to M. Delafond, a professor of the school at Alfort, the task of investigating this malady, commonly called the 'blood disease,' in the districts in which it was raging. He was to search out its causes, and ascertain whether they did not result from the system of cultivation prevalent in the country.