Blood-poisoning can never be a trifling thing. We should be in deadly danger of it every day, but that so much is arranged in our bodies not only to prevent it, but to relieve it promptly when it begins to take place. Indeed, each particle of used-up matter, which has served its purpose in any organ, becomes poisonous the moment it gets into the blood. But then, at once, the lungs, skin, kidneys, and bowels, with help also from the liver, take from the blood these dead particles, and carry them out, in the exhaled breath, perspiration, urine, and excrement.

There are several forms of blood-poisoning, due to suppression of the action of the kidneys, nonsecretion of bile by the liver, or to retention of putrefiable matter not carried off by the bowels.

Next to these may be named septicaemia, produced by the absorption of foul material from a surface of the body, or near it; as from a gangrenous wound or an unhealthy abscess. Outside poisons reach the blood through the mouth and stomach, by the lungs, or by the skin, as by bad drinking-water, and the microbes of malaria, smallpox, scarlet fever, yellow fever, cholera, etc.