Excerpt from Applied Immunology: The Practical Application of Sera and Bacterins Prophylactically, Diagnostically and TherapeuticallyNatural I mmunity. - The natural or spontaneous resistance of the animal organism to disease is only relative, never absolute. The ability of animals toward of disease varies with different species and among individuals of the same family. Under nor mal conditions, an animal may be protected indefi nitely from infection. Nevertheless, if his vital resis tance be permitted to fall or he be exposed to a viru lent infection, his defences may crumble instantly and disease be contracted. On the other hand, the natural immunity of certain species to infection is remarkable the negro to yellow fever and most of the lower ani mals to the venereal diseases.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.