Page:Popular Science Monthly Volume 26.djvu/640

622 are frequently and deeply flooded over, and yet the cholera never comes!

Just as the disposition to cholera in time and place may be due to two causes, so may the immunity from cholera be dependent either on the physical nature of the soil, as is the case in parts of Traunstein and Kienberg, or on the condition of the soil as regards moisture, as happened in the low-lying parts of Munich during the summer epidemic of 1873, or at Augsburg during the summer and winter of 1873, or at Munich in 1866. Such a degree of wetness as prevailed on those occasions may be a constant condition in some places; to this latter group the low-lying districts of Lyons belong. Indeed, both factors are at work in Lyons. In the high-lying parts the granite comes to the surface in many parts, and so a very efficient and natural drainage is secured. These districts may always be said to be free from cholera. The soil of the low-lying parts, situated on the banks of the Rhone, Brotteaux, Guillotière, and Perroche, has always a certain degree of humidity, which cholera when imported has to encounter. This moisture of the soil of parts of Lyons is dependent not only on rain, but also on the river Rhône. The impermeable bottom of its bed is of solid granite, to which fact I could bear personal testimony. This stratum of granite stretches from the left bank of the Rhône far inward, so that Lyons is built upon it; all the springs lie below the level of the surface of the waters of the Rhône, and so rise and fall with the river. In Paris, in Munich, and in Berlin the conditions are otherwise. Here the level of the subsoil water is above the level of the waters of the Seine, Isar, and Spree, respectively; this relation is the most general, so that Lyons is exceptional. In Lyons it may be said that a part of the Rhône runs subterraneously, so that the soil receives water from the river; whereas in Paris, Munich, and Berlin the direction of the water is constantly from the soil to the river. When the water rises in the beds of the Seine, Isar, and Spree, there is no penetration of the water into the porous soil, but rather a damming and stagnation in the discharge of the subsoil water. The granite of the Rhône, chiefly composed of large blocks of quartz, contains also much fine sand, which is able to suck up water to a considerable height in its capillary spaces, possibly as high as the zone of evaporation. I investigated the hardness and moisture of this quartz by actual digging. This part of Lyons is only at times free from cholera, and would be susceptible of an epidemic were some of its water taken away. That Lyons may be fatally visited was shown in the year of cholera, 1854. As I was studying the conditions of cholera in Lyons, I found that in 1854 no less than 500 deaths occurred from the disease; while at other times the town escaped with a dozen deaths. It also transpired that nearly three fourths of the deaths happened in Guillotière, and I must say, therefore, that in the year 1854 at least a part of Lyons suffered from an epidemic of cholera. The Lyonese were not pleased with this