The principles underlying the treatment of disease have in the past been matters of speculation only. What was known to do good had been found to do so empirically, and was handed down from one generation to another in the most dogmatic way. With the birth of the germ theory of disease speculation gave way to exact science, and it became possible to base plans of treatment upon rational theories. In the light of the germ theory of disease, immunity becomes the fundamental principle underlying all treatment of those diseases which are due to living organisms. The usefulness of a plan of treatment must therefore be predicated upon what it will contribute toward maintaining or bringing about immunity.
Certain axioms can be formulated out of our present clinical and laboratory knowledge of germ diseases. These are: 1. That all germ diseases are due to parasitic life of living organisms. 2.