The present is preëminently the time of the study of the etiology of disease, just as the past has been characterized by an almost exhaustive study of anatomy, physiology and pathology. In this connection the subject of infection has been the most profitable, as it hae been the most interesting of all investigations; most interesting because little by little it has brought to light the knowledge of microörganisms that produce diseases, the causation of which was hitherto inexplicable; profitable because it has and will result in the discovery of the conditions that arrest their development and the agents that will neutralize their toxic influence.
Infection from without we may safely say produces the various forms of meningitis, including cerebro-spinal meningitis, tetanus, hydrophobia, acute poliomyelitis, acute ascending paralysis, the puerperal and syphilitic diseases of the nervous system.
The infections which arise from within are also important etiologic factors in developing diseases