In ordinary parlance we speak of the etiology of disease, but for us these old school ideas are far too narrow because the radius from which we draw our information is wide and may include any influence whatsoever. Things, in themselves apparently very trivial may become of the greatest import when related to the beginnings of disease. Sickness arises from extrinsic as well as autogenetic causes.
The former are in a general way more accessible and therefore more accurately defined. They embrace the susceptibility to certain external influences which pervert the vital force, injuries, the state of the weather, heat, cold, dampness, physical exertion, etc.