II. MODES OF PROPAGATION.
HAVING now discussed the relations in time and space which predispose to cholera, I shall pass on to consider those relations in regard to the freedom from cholera which they may enjoin. Places which enjoy an immunity from cholera are more numerous than was formerly supposed, but have been less studied from a point of view of epidemiology, just as relations in time have been but little investigated. The eye of the investigator has only fixed itself on the places where, and at the time when, cholera has reigned. We ought likewise to investigate the matter when and where cholera does not exist. Ordinarily a physician only bestirs himself when he is called to see a case. It has, however, not been so with me. Impressed with these notions, I went in 1868 to the place in Southern France which had enjoyed the greatest and most renowned immunity from cholera. Through the kindness of M. Fauvel, I was introduced to M. Luuyt, of Lyons. Although Lyons was in frequent communication with Marseilles and Paris when epidemics of cholera raged, yet the disease never showed itself in an epidemic form at Lyons. In 1849, for instance, Lyons was besieged, conquered, and invested by troops suffering from cholera. Then the town escaped, while the soldiers suffered severely. This immunity was certainly not due to greater cleanliness of that quarter of the town known as Croix Rousse; nor was it due to the social misery or to the wants of the working-classes; neither had the drainage or water-supply, which prior to 1858 was as bad as it could be, anything to do in the matter. So that the immunity was probably the result of natural conditions. The Lyonese had often congratulated themselves on this excellent gift of nature, but it is probable that the constant movement of air which the combined flow of two great rivers (the Rhône and the Saône) originate is the cause of the immunity, although the mistral (Mistralstürme) which scours Languedoc and Marseilles had never been able to drive the cholera away. The situation of Lyons is far different: the bed of the two rivers is composed of compact granite, which on the right bank of the Rhône and on both banks of the Saône rises high, being in places coated with lias, molasse, and thick mud strata. On the heights lie the parts of the town called Croix Rousse, Fourvière, and St. Juste; other quarters lie low—Perroche on a tonarue of land between the two rivers, Lvon Vaise on the right bank of the Saône, and Brotteaux and Guillotière on the alluvial soil of the left bank of the Rhône. The lower parts of Lyons
- Reprint of a special translation made for the London "Lancet."