It may be communicated from the sick to the healthy (1) by persons suffering with the disease; (2) by bodies of persons that have died of smallpox; (3) by infected articles; (4) by healthy third persons; (5) by the air, to persons living even at some distance; (6) by inoculation. The poison enters the body by the mucous membrane of the nose, mouth, or respiratory tract, and probably through the mucous membrane of the stomach and through the broken skin. Patients can communicate the disease probably during the period of incubation (from 5 to 20 days after exposure to the disease--commonly about 14 days); and certainly from the initial stage until no trace is left of the final skin-desquamation. The infection is most active during the formation and duration of the pocks. The mildest smallpox in one person can cause malignant smallpox in another, and _vice versa_. The mortality in the unvaccinated is between 40 and 50 per centum. A typical case of confluent smallpox at its height is the {173} ugliest disease in appearance and stench and almost in substance, known to medicine. Anyone liable to infection by it, or likely to carry it to others, who says he is "not afraid of it," has either never seen it and he is talking childish nonsense, or he has seen it and he is a fool. The face is a bloated mass of corruption; the eyes are swollen shut; the nose, cheeks, lips, and neck are puffed out enormously; the mouth is a large sore, ulcerous, and spittle trickles from it ceaselessly. The fever is up to 103 or 105 degrees; there is an unquenchable thirst, a vile stench, sleeplessness; often delirium is the only relief, and there is one chance in two of a disfigured recovery. Tobacco, alcoholic liquor and a walk in the fresh air will not disinfect the visitor to such a disease. Years ago I investigated in the laboratory the popular notion that tobacco is a disinfectant. I found that bacteria, the diphtheria bacillus and swarms of others more delicate, will grow as well in the presence of a large piece of "Navy Plug," as when tobacco is absent. Chewing tobacco, whiskey, a walk in the fresh air as disinfectants, the Sioux medicine-man's powwow, the hind leg of a rabbit as a charm, are all in the same category.