Their pestilential character, their extended influence, and their great fatality, rendered their appearance and progress a special terror to physicians, and melancholy apprehension to the people. They seem to have been regarded as the manifestation of an invisible power, which directed and guided "the pestilence that walketh in darkness" and "the destruction that wasteth at noon-day;" a visitation or chastisement over which human ingenuity and medical skill had little control. Under these impressions, the earlier physicians labored and endeavored to satisfy the great mass of mind that these occasional and special developments of disease arose from natural causes, and were subject to certain natural laws. They ascribed their origin to the commingling of some specific poison in the food, and drink, and air, which, through these "media," was received into the system. Subsequently, they seem to have made some advance on this theory, and considered the extreme Summer heat--especially the intense heat of the sun in a dry season--the emanations from stagnant waters, and the miasm exhaled from the soil, and from putrid bodies of animals, as the chief causes of all epidemics. These views prevailed for a very long period, and have undergone no very remarkable change from the observations and discoveries of centuries. Modern and quite recent writers have advanced nearly the same doctrines, embracing, however, the principal sources of insalubrity--the malarious and miasmatic influences; and have assigned as the cause of epidemics, especially that of Cholera, a peculiar constitution of the atmosphere, and certain predisposing causes combining with each other, so that an association or union of these two independent and individual causes are necessary and essential to the production of the disease.