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It took the world a long time to come to the idea of the communication of disease by actual contact with those suffering from the disease, or with something that had been so close to them as to carry contagious elements with it. It is very hard to understand at the present time how this precious knowledge, seemingly so obvious, was so long delayed. Practically only one disease— smallpox—was definitely known to be due to actual contagion or to personal contact with a patient or his secretions before the beginning of the nineteenth century. People thought that epidemic disease was due to something in the air, or atmospheric conditions were considered to influence certain natures in such a way as to produce particular diseases in them. When we speak of psychic contagion in our own time, most people are apt to look on the expression as eminently figurative and as
PSYCHIC CONTAGION OF CRIMINAL IMPULSE.. JAMA. 1907;XLIX(7):601-602. doi:10.1001/jama.1907.02530070071005