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300 by such germs, and it has been shown with a great degree of probability that such contamination frequently results from the transportation of infectious material from the surface of the ground, from shallow pits, etc., by flies, which after visiting the most filthy places, may alight upon a beefsteak or fall into the milk jug in a well-ordered kitchen. But by far the larger number of cases result from drinking water containing the cholera germ.

The epidemic extension of cholera depends upon climatic conditions to a much greater extent than does that of typhoid fever. It is especially a disease of hot climates, and of the summer months in temperate regions. The disease may be propagated during the winter, even in cold climates, by the occurrence of a series of cases in localities especially favorable for such propagation, and in this case a recrudescence of the epidemic usually occurs during the following summer. In Russia, during the years 1853 to 1855, nearly two hundred and fifty thousand deaths occurred during the months of June, July, August, and September, and less than twenty-five thousand during the remaining months of the year. In 1832 cholera was introduced into Canada by emigrants from Ireland, and spread rapidly in the valley of the St. Lawrence. An independent importation during the same year brought it to New York and to New Orleans, from which points it obtained a tolerably wide diffusion in the United States. In 1835 it appeared for the first time in South America, on the coast of Guiana. North America was again visited by the scourge in 1848, and it continued to prevail in the United States and Mexico for several years, especially in 1849 to 1850. In the West Indies it caused a considerable mortality in the period from 1850 to 1854. During the year 1854 it again became widely prevalent in the United States. In 1865 the West Indies suffered from another severe epidemic, and in the following year the disease again established itself at three widely separated seaports in North America—Halifax, New York, and New Orleans. From the last-mentioned port it extended throughout the Mississippi Valley. During the years 1865 to 1868 the disease also committed great ravages in some of the South American countries not previously visited by it, and especially in Brazil, Paraguay, Uruguay, and the Argentine Republic. In 1873 cholera was again imported to New Orleans and spread throughout a considerable portion of the Mississippi Valley. Our exemption from an epidemic during the recent widespread prevalence of the disease in Europe is, no doubt, due to the efficient methods for its exclusion adopted at our ports of entry, and especially at New York, where several cholera-infected ships arrived during the height of the Hamburg epidemic of 1892.

Yellow fever is essentially a disease of the littoral, and especially