As we note the army of workers in the field of bacteriology, and the vast amount written on the subject, we can hardly realize that it has been scarcely twenty years since the germ was first demonstrated as the cause of a disease, and less than three years since Behring and Roux published perfected methods for preparing and administering diphtheria antitoxin. During this short period of discovery, recognized but unexplained truths have been elucidated, and many new facts have been brought to light. Many of the facts of immunity have been known since prehistoric ages, but prevailing theories regarding these questions were at fault: consequently, clinical interpretations and treatment have been fallacious.
Before studying the antitoxins, it will be well to take a brief historical survey of the knowledge already acquired regarding the facts of immunity and the theories put forth to explain these facts. Pasteur in 1880 began his