The germ theory contains much truth, but in the very large percentage of cases where the micro-organism is a factor its significance is only of secondary consideration. Immunity and resistance comprise an important part of the health problem, of which the intact anatomical is of first consideration. Usually the micro-organism plays the role of an exciting and determining factor; before it can multiply and grow there must be a field that is first nutritionally disturbed. Nutrition of the tissue is the one great point always to be considered. The constitution of an individual is the pivot about which predisposing, environmental, and exciting factors of disease center. Health represents the integrity of the artery as well as a maintenance of that master tissue, the nervous system, and anything that produces or influences, directly or indirectly, a disturbance of physiological functioning borders on the pathological. Hence the osteopath recognizes many of the common medical causes of disease, but reserves the privilege of rearranging their relative positions, for the osteopathic cause of disease greatly modifies their value. =Osteopathic Etiology= distinctively emphasizes structural derangements and perversions. Of =first= importance, owing to static requirements, is the =osseous lesion=. This lesion is represented by any abnormal change of position or relation of the many bony constituents of the body. The framework of the body is subject to not only any and every physical violence of any mechanism, but moreover being the corporeal foundation of a vital mechanism is subject to both direct and indirect biochemic changes and influences. Thus the osseous lesion is caused (a) by traumatism, e. g., strains, falls, blows, etc.; (b) indirectly by atmospheric changes, over and violent exercise, the slumped posture, debilitating habits, etc., through the media of muscle changes and imbalance; (c) by nutritional effects disturbing the elements of bony tissue; (d) by ligamentous change such as thickening of a capsular ligament; (e) by infections; (f) compensatorily and reflexly through the media of body distortions and muscular irritability or debility, e. g., an innominate lesion may be compensatory to a lumbar curvature, dietetic errors may cause dorsal muscular irritation and contraction produce a constant osseous lesion which in turn may result in chronic indigestion.