As a result of the work of Pasteur and the numerous investigations which have followed in the same line, it is now generally believed by bacteriologists that many diseases, especially those which seldom affect individuals more than once, are self-limited by the formation within the blood of a product capable of destroying the toxic material that excites the disease, hence called antitoxin. In such diseases if life be prolonged until a sufficient quantity of the antitoxin has been developed the toxic agent is destroyed and recovery follows if no serious complications have arisen.
In diseases that can be communicated from man to animals and vice versa, such for example as rabies, anthrax and diphtheria, advantage has been taken of this fact by inoculating animals with the attenuated toxic principle in small but steadily increasing quantities until an antitoxin is developed in the blood in sufficient quantity to render the animal
INGALS EF. ORRHOTHERAPY IN DIPHTHERIA.. JAMA. 1896;XXVII(1):1-4. doi:10.1001/jama.1896.02430790001001