Nearly all substances which produce a marked irritation in the upper gastro-intestinal tract are likely to induce vomiting. Under these extreme conditions the emesis represents a useful protective device of the organism, evidently intended to expel the offending substance from the alimentary canal. Quite aside from such more exceptional cases of local attack on the mucosa of the stomach and intestine, a variety of drugs used even in comparatively small doses provoke the act of vomiting as well as the attending or premonitory symptom known as nausea. Some substances, like the familiar apomorphin, act as emetics after introduction subcutaneously into the body as well as by oral administration. To explain this on the assumption of a purely localized stimulation within the gastro-enteric canal it is necessary to assume that the injected drug is actually secreted into the lumen of this tract.
The hypothesis of an irritant action on the alimentary