ing into the presence of the sick one, while the truth is he may carry the germ under his finger nails or elsewhere about him, and there is no telling when it may first find its way into his body. We can determine the period of incubation in the lower animals by inoculation, and here we know that it varies greatly with the method of inoculation, the virulence of the germ, the number of germs introduced, and the susceptibility of the animal. All that may be said about the period of incubation in man is of but little value. The same is largely true concerning the extent to which the disease is contagious. In the epidemic of 1835 in Egypt only one of the French physicians who attended the sick contracted the disease. Bulard, who did not believe the plague contagious, wore for two days a shirt taken from the body of a dead man. He remained well, and thought that by this he had demonstrated the truth of his theory. Such experiments demonstrate nothing. There is no evidence that any of the bacilli were on the garment, or that, if they were, they were introduced into his body. During the epidemic in Hong Kong, fifteen European physicians and a number of Chinese medical students cared for the sick in the hospital, and none acquired the disease. This only shows that with care and cleanliness the sick may be attended without danger of infection of the attendants. Hundreds of bacteriologists in laboratories are daily handling the most virulent cultures of the diphtheria bacillus, and the first case of infection from this source has yet to be reported. This does not prove that these bacilli are not pathogenic to man, or that these men are insusceptible to the disease. Because an expert handles the most venomous serpents without being bitten, does not prove that the bite of these reptiles is harmless.
The exaggerated idea of the contagiousness of the plague held by some of the older writers is exemplified in a graphic way by the following quotation from Hecker: "Every spot which the sick had touched, their breath, their clothes, spread the contagion; and, as in all other places, the attendants and friends who were either blind to their danger or heroically despised it, fell a sacrifice to their sympathy. Even the eyes of the patient were considered as a source of contagion which had the power of acting at a distance, whether on account of their unwonted luster or the distortion which they always suffer in plague, or whether in conformity with an ancient notion, according to which the sight was considered as the bearer of demoniacal enchantment."
The plagues of the middle ages were undoubtedly spread by the processions of the Brotherhood of the Cross. These fanatics went, sometimes in great numbers, from place to place, praying for the sins of the world, and scourging themselves with leathern straps armed with points of iron.
