Like most disease-germs our wound-infection foes are literally "they of our own household." They don't pounce down upon us from the trees, or lie in wait for us in the thickets, or creep in the grass, or grow in the soil, or swarm in our food. They live and can live only within the shelter of our own bodies, where it is warm and moist and comfortable. This is one great (in the expressive vernacular) "cinch" that we have on the vast majority of disease-germs, whether medical or surgical, that they do not flourish and breed outside of the body, or of houses closed and warm; and this grip can be improved, with skill and determination, into a veritable strangle-hold on most of them. In the language of biology, most of them have become "adapted to their environment" so closely that they can scarcely flourish and breed anywhere outside of the warm, moist, fertile soil of a living body, and many of them cannot even live long at temperatures more than ten degrees above or fifteen degrees below that of the body. At all events, so poorly are these pus-germs able to preserve their vigor and power of attack, not merely outside of the human body, but outside of some wound or sore spot, that it is practically certain that eight-tenths of all cases of wound-infection or blood-poisoning come directly from some previous festering wound, sore, ulcer, scab, boil, or pimple, in or on some other human being or animal. Practically whenever we get pus in a wound in a hospital, we insist upon finding the precise previous case of pus from which that originated, and seldom is our search unsuccessful. If we kept not only our wounds surgically clean, but our gums, noses, throats, skins, and fingernails, and burned and sterilized everything that came in contact with a sore, pustule, or scab, we should wipe out nine-tenths of our cases of wound-infection and suppuration; in fact, practically all of them, except such small percentage as may come from contact with infections in animals. This is the reason why, up to half a century ago, by a strange paradox hospitals were among the most dangerous places to perform operations in, on account of the abundance of wounds or sores always present for the pus-germs to breed in, and the fact that out of fifty or more wound-cases, there was practically certain to be one or two infected ones to poison the whole lot.