A toxin is a poison produced in our bodies by germs or bacteria that cause certain kinds of disease. An antitoxin is something that works against this kind of poison. Diphtheria, cholera, scarlet fever and tetanus (lockjaw) are among the diseases caused by toxins produced by germs. Our bodies manufacture sources to fight off these toxins and make them harmless. These substances are called antitoxins. Enough antitoxin is usually manufactured by our bodies when we have a mild case of a disease that is caused by a toxin.
Sometimes there is too much toxin present and our bodies need help. Doctors give this help by injecting antitoxin into us when we need it. The antitoxin comes from the blood of an animal that has been given the disease. The animal is ill for a short time and soon recovers. After recovery the animal's blood contains a large amount of antitoxin. The antitoxins taken from the blood of such an animal are used to help people who have that particular disease. Diphtheria germs are injected into horses. The horses' bodies build up antitoxins to fight off the diphtheria toxin.
The antitoxins in their blood are injected into people who have diphtheria, and also to help people avoid catching diphtheria. A person who has received an injection of antitoxin will rarely catch the disease and be made sick by it. The antitoxin attacks the toxins of the disease as soon as they enter the body and renders them harmless before sickness sets in. The modern medical way of avoiding disease is to use something called toxin-antitoxin. The toxin injected into our bodies in this mixture makes it possible for our bodies to start manufacturing antitoxin. The antitoxin injected in this mixture makes sure that the toxin does not become so strong in our bodies that it will make us sick.