Offensive odor of the breath is often a matter of considerable importance to those afflicted, and medical advice is occasionally sought. The fact that the odor may arise from pathologic conditions in the structures of the mouth and respiratory tract is well recognized. But in many cases no definite pathologic changes are found. Moreover, the odor may not be present continuously but only during temporary periods of disturbed health or during menstruation. It has been suggested that in such cases the substances causing the odor are of systemic origin; that the air in the lungs is tainted by aeration from the blood, or in the mouth from secretion of the substances into the saliva; or, again, that the odor arises directly from the stomach. It is more probable, however, as the evidence to be here presented also indicates, that generally the source of the odor is not systemic but local