Mr. Editor: - The followüig instanees Ilustrativa of the influonce of at least one of the sourees of epidémica possess an intrinsie and general interest at all timosrand especially in the present unhappy coudition of our country; and commend theiuselves to the attention of organiza! ions liaving iu charge the sanitary eondition of the country, viz : In 1566 an epidemie distemper broke out ainongst the imperial army encamped near the Danubo, in the vicinity of Komorn, aud below Presburg, during the war which Maximillian the Second carried on agaiust the Turks. The disease followed the army during its subsequent movements. Sorae convalescent men that wero sent homo propagated the disease all over Germany, and Vienna, whicli was on the high roatl of the returning soldiers, Buffered considerably. In the summer of 1621 a severe epidemie appeared among the allied troops encamped at Weidhausen, and spread' to the Palatiuate and upper Bavaria. It was couveyed frora the soldiers to the inhabitants, without distinction of age, sex, or rank. At the siege of Louvain, 1655, the army of Louis the Fourteenth bfiing short of provisions and. destroyed by disease, was foroüd to retire to Nimeque. The epidemie entered tho city with the soldiers, made frightful havoe amongst them, and did not spare the inhabitants. Eveu the conventa suffered considerably. Ozonam un.-ntions that the French troops sent iuto Lorraigne after the siege of Philipsburg, carried into that proviuee a malignant and coutagious fever. Duriug the siegea of Prague and Egra defended by Marshall Bellisle, an epidemie disease of severe type appeared araong tho troops and inhabitants The Prussiun army becamo also iufeoted, and in retiring into Silesia, apread oontagion among the rest of the troops and the population of the province. Infectious diseases broka out in the French army during the Spanish campaign of 1808 aud 1809. The diseates were conveyed to Franco by prisoners oud the niarch of troops. Euglaud also suft'ered wheu the Euglish troops returned home. Epidemie dysentery reigned at Lyons in 1624 and 1625 the disease having been brought by the troops returuing from Italy ; and in 1757 the Frenoh arniy, which passed through the electorate of Mayeuoe, spread dysentery amongst the iahabitatits alotig the whole line of march. The town of Mayence sufifered inoro partioularly. The annals of medicine furnish numerous other instancea of the influence of discasea generated by camp life in giving origin to wide spread epidémica.