The object of quarantine is to prevent the introduction of epidemic diseases from one country into another, and its regulations are based on the assumption of the contagiousness of the diseases with which it deals; it being supposed that such diseases are propagated by contact, direct or indirect, of the unaffected with the affected. In accordance with this view the preventive means adopted by quarantine consist of the isolation of the sick or suspected, with whom it interdicts all communication, whether by person or by articles deemed capable of transmitting contagion. When quarantine was first established, the spread of epidemic diseases exclusively or chiefly by contagion was a doctrine universally received;[25] but during the last century a change has gradually taken place in professional opinion in almost every country in Europe, particularly in France, Russia, and Austria, as well as in America, with respect at least to several of these diseases, chiefly by medical officers, who, having had the charge of the health of fleets and armies in different quarters of the globe, have been under the necessity of studying the circumstances connected with the outbreak and spread of formidable epidemics; and also by those who, having had the care of hospitals and dispensaries in large cities, have been obliged to visit the localities and abodes of the poorer classes, where these diseases are always the most prevalent. Footnote 25: The wide difference between the qualifications of the accomplished popular physician and the scientific investigator into the causes of epidemic sickness was strikingly exhibited in the first outbreak of Asiatic cholera in 1831, when the emergency required not merely a knowledge of the practice of medicine, but the power also of applying the philosophy of public health to the exigencies of the moment. How were these exigencies provided for? A board, comprising all the most eminent and skilful physicians of the day, was assembled in the College of Physicians, under the presidency of Sir Henry Halford; and, after declaring, in opposition to the unanimous opinion of the physicians of Bengal, “that no measures of external precaution for preventing the introduction of the cholera morbus by a rigorous quarantine have hitherto been found effectual,” they issued the following official notification:—