Canine anaphylactic shock, peptone shock and histamine shock are currently assumed to be physiologically identical reactions. In each shock there is a sudden, pronounced fall in arterial blood pressure, the carotid pressure being reduced to about 25 mm. Hg. by the end of two minutes. Recovery usually begins about the tenth minute, the arterial pressure being restored to normal in from 30 minutes to 90 minutes, depending upon the severity of the reaction. In each shock, fatal results may be produced by the injection of large doses or by the use of highly sensitized animals. In each shock there is a pronounced splanchnic engorgement and cyanosis, the production of hemorrhagic lesions in the intestinal mucosa, and a reduction in blood coagulability. In order to test the assumed physiological identity of the three shocks, we have endeavored to determine the topographical distribution of the dominant reacting tissues in each shock.1. Canine anaphylactic shock. Anaphylactic shock (fall in arterial blood pressur...