Page:Popular Science Monthly Volume 26.djvu/521

Rh took cholera from India, Arabia, Afghanistan, or Persia, through couriers and stage-coaches. It soon became clear that cholera, the specific cholera-germ, was in some way or other propagated along the paths of human intercourse, and it also became evident that unless the germs found a suitable soil within a certain time they did not flourish. Observers soon discovered that cholera was more prone to appear in certain regions and to affect certain localities, while it shunned other districts; and, again, that other regions were only visited at intervals of many years. It is also a fact that Asiatic cholera never yet appeared at a place which had not previously been in communication with a region where cholera prevailed; and, further, that the disease from an infected locality never yet passed on to another place if the journey lasted a certain time without interruption. The large intercourse between India and Europe, more particularly England, by means of ships which sailed round the Cape of Good Hope, had never succeeded in carrying cholera from India to England; it was only by the overland route that cholera reached England. Neither had the Cape or Australia ever been visited by cholera. It is possible that in the future the communication may be so much accelerated that cholera may get to these countries. In much the same way South America escaped during the epidemic (1830-1840) in Europe and North America. It was supposed that in South America yellow fever was enough to prevent cholera, or that this disease kept out cholera, until suddenly, in 1854, after a service of fast sailing-vessels between Philadelphia and Rio de Janeiro had been established, the chief town in the Brazils experienced a terrible epidemic of cholera. When cholera passes overland it dies out unless it finds a suitable soil within a certain time. Rainless deserts are unfavorable to cholera. Caravans which pass from infected localities through deserts have never spread the disease, provided the journey in the desert lasted at least twenty days.

Cholera always requires for its propagation favorable stations on land, and, as a rule, if the course of epidemics be traced, a gradual extension in successive years is found to take place in fixed directions. In the east and southeast of Russia, for example, cholera prevailed after it bad raged in Persia in 1868; in 1869 eleven, and in 1870 thirty-seven provinces were affected, and among them five districts in Poland. In the year 1871 the epidemic spread into the west, east, and north of Russia, and succeeded in reaching East Prussia, when Königsberg was severely visited, so that from July 24th to November 8th, 2,012 individuals died there of cholera; while in Berlin only fifty-two and in Potsdam only seventy-one succumbed. In 1872 the epidemic reached Eastern Hungary, and in the following years reaped rich harvests in Germany. It has rightly been said, therefore, that cholera does not travel quicker than man. Nevertheless, the spring-like mode of progression of cholera is noteworthy: for example, it regularly jumps from Marseilles to Paris, or vice versa, passing over