When the horse was well, the doctors gave him more of the poison; this time he was not so sick and got well even more quickly. This treatment with toxin was repeated in gradually increasing doses until the poison did not affect the horse at all. Then the doctors said, "His blood is full of antitoxin, and we will see what it will do when injected into some other animal." So they drew off some of the horse's blood and took out all the little red cells, leaving nothing but the clear fluid of the blood. They planted diphtheria germs in a rabbit's throat, and when the rabbit became very sick, they gave him some of the antitoxin from the horse. The rabbit immediately got well. Afterward they gave some of this antitoxin to a little boy who was very sick with diphtheria, and he, too, got well. Ever since then the doctors have been saving many lives by the use of antitoxin. [Illustration: FIG. 56. Showing the number of deaths in 100 cases of diphtheria when antitoxin is used on the first, second, third, fourth, and fifth days.] [Sidenote: Evidences that antitoxin saves lives] Someone may ask, "How do we know that it is the antitoxin that saves lives?" In just this way: before we knew anything about antitoxin, about half of all the people with diphtheria died; but since we have had antitoxin, only about twelve die out of every hundred who have this disease. More than this, we know that when the antitoxin is given within the first twenty-four hours after the patient is taken sick, there is only about one death for every one thousand cases of diphtheria. Do you not think that this is strong proof that antitoxin saves lives? [Sidenote: How antitoxin saves lives] Antitoxin saves lives not only by curing those who have diphtheria, but by preventing others from having it. If a person who has been where there is a case of diphtheria is given a dose of antitoxin, he will not have the disease, because his blood will contain enough antitoxin to destroy the diphtheria toxin present. If you will watch a careful doctor when he makes his first visit to a case of diphtheria, you will notice that, as soon as he gets through treating the patient, he gives all members of the family who have been near the patient a dose of antitoxin to keep them from getting sick. [Sidenote: Antitoxin not a poison]