The belief in the infectivity of phthisis is as old as any extant account of the disease. Hippocrates said that it was of all diseases the most dangerous, and fatal to the greatest number of mankind. Paris in the fifteenth century, noted the frequent occurrence of phthisis in those who tended consumptives. In Italy the belief in the infectiousness of phthisis took practical form in legislative enactments. Civil, religious, and military authorities shall cause to be burned in civil and military hospitals all linen which shall have been used by phthisical civilians or soldiers. In 1754 the members of the college of physicians of Florence pronounced themselves as on the whole favouring the conclusion that phthisis is communicable. The histories of cholera and influenza present similar anomalies. Tuberculosis differs from them in infectivity chiefly in its longer latency and more protracted course.