All around us there are invisible forms of life which we call germs. They are in the air, in the soil, in the water we drink and the food we eat. Many of them are harmless or even beneficial to man, but others may cause diseases. The human body has many natural weapons to fight off the attack of the harmful germs. For instance the digestive juices and the blood itself kill of many kinds of germs. But certain ones enter the body and start an infection. Then the antigerm “soldiers” in the body spring into action. These are the white corpuscles in the blood. They can pass right through the thin walls of blood vessels and they can wander all over the body. The white blood corpuscles gather at the point of attack and destroy the germs by feeding on them.

But disease isn’t always caused by a direct attack of germs. Germs throw off a chemical substance called a Toxin which acts as a poison in the body. Once again, the body has a built-in defense. The toxin causes certain cells in the body to go to work to produce a substance that destroys the toxin. This is called an “antitoxin.” If the antitoxin produced quickly enough and in enough quantity, the germ poison is neutralized. The body gets well.

This antitoxin is always a very special one that works only against the toxin for which it was produced. It remains in the blood for some time alter the toxin has disappeared. Now suppose the same germ attacks the body and produces new toxin. Instead of becoming sick, we show no symptoms or the disease at all! The reason is that our body already has a resistance to the disease; it has the antitoxin act ready We call this condition “acquired” is Immunity. It is “acquired” because our resistance came after the original attack of the germs.

Now let us suppose there is an attack of germs upon the body, spreading toxins through our system, and yet we don’t get that specific disease. This means our blood had enough antitoxin in it to begin with to prevent the specific poison from doing any harm. We call this a “natural” Immunity. It is a quality of our blood that we inherited.

If we introduce a little toxin in our blood so it can produce antitoxin to prevent disease we call it artificial immunity. This is exactly what happens when we are vaccinated against diphtheria and typhoid.