There are many diseases in which the symptoms are caused, not by the bacteria themselves, but by the chemical poisons the bacteria manufacture. Thus, in tetanus, or lock-jaw, the bacteria grow, perhaps unnoticed, at the bottom of the Fourth-of-July wound on the hand or foot; but the chemical poisons they manufacture, carried by the blood to the brain and spinal cord, cause the spasms and convulsions that characterize the disease. In diphtheria, the bacteria rarely enter the body, but grow in grayish-white masses on the moist surfaces of the mouth and throat. The chemical poisons they manufacture, absorbed by the tissues, cause the paralysis and heart failure that characterize the disease.
The body has the power of forming substances that neutralize these poisons. To these neutralizing substances the name antitoxine has been given.
This fact is of hygienic importance for two reasons. First, because it is sometimes possible to assist the body in its efforts to form antitoxines, by introducing into it antitoxines artificially prepared; and, second, because the body's power to form these substances is modified by mode of life. A horse that has been repeatedly injected with poison manufactured by the germs of diphtheria growing on an artificial culture medium, develops enormous amounts of diphtheria antitoxine. A few drops of its serum will render harmless large quantities of diphtheria poison.[1] Overwork, insufficient clothing, improper food, alcoholic excesses, lack of sleep, and other factors, so lower the antitoxine-forming power of the human body, as to greatly increase the dangers from infection.
The second way of hygienic importance in which the body fights disease is by the formation of chemical substances that, although they have no influence on the poisons manufactured by bacteria, have an even more important property, that of killing the bacteria themselves. The presence of these antiseptic, or bacteria-killing substances in the blood and tissue juices is easily shown. One has but to mix bacteria with serum, and test, from time to time, by simply cultural methods,[2] whether or not the bacteria are alive. Thus, in one experiment, there were mixed with human serum germs of typhoid fever in such numbers that every drop of the serum contained 50,000 bacteria. Two minutes later, but 20,000 of these were alive; at the end of ten minutes, but 800; and in twenty-five minutes, they were all dead.
Not only can serum kill bacteria, but most of the secretions of the healthy human body are bacteria-killing as well. Gastric juice, vaginal secretion and nasal secretion, kill bacteria in enormous numbers. The
