In its physiological action the poison of _Latrodectus mactans_ resembles angina pectoris vasomotoria--a purely functional derangement. The similitude of the physiological action to pure angina pectoris corroborates the accepted pathology of the latter condition, because the phenomena of _Latrodectus_ poisoning were educed from previously healthy organisms, and in pure angina pectoris there is no pre-existent organic change occasioning the attack. According to the accepted pathology, we have in angina pectoris vasomotoria, sudden spasms of the arterioles; from this an increase of the arterial tension; to overcome this is more forcible and rapid action of the heart; as the arteriole spasm persists and doubtless deepens in intensity, distension of the left ventricle follows, and from overdistension the agonizing breast-pang, and even death from stoppage of the heart's diastole. But we must include another element--spasm of the coronary vessels. "When there is a sudden rise in the blood-pressure in the arteries, due to vasomotor spasm of the peripheral systemic arterioles, and the heart-walls are strong and well nourished, palpitation is evoked; when the coronary branches are involved in the vasomotor spasm then angina is produced, and the heart-walls, acutely distended with blood, can scarcely contract in the face of the opposition presented to their contraction by the high arterial tension. When this sudden systemic arteriole spasm extends to the coronary vessels in a heart whose walls are diseased, a fatal attack of angina with the heart full of blood may be induced. The danger increases with the extent of the structural degeneration of the heart-walls. Sudden rises of blood-pressure in the arteries will tax hearts in their textural integrity, and lead to painful distension; such sudden demands on decayed hearts lead to agonizing angina pectoris, and the sense of impending dissolution is frequently followed by sudden death." Spasm of the arterioles and coronary vessels, rise of blood-pressure in the arteries, embarrassed action of the heart, and painful distension are just so many consecutive links in the phenomena produced by the poison of _Latrodectus mactans_, as Cases I and IV amply testify. The spider poisons are akin to the serpent poisons in their property of producing a disorganization of the blood. In Case I, thin and florid non-coagulable blood continued to ooze from the cut surface despite the application of tannin. It may be a question whether this condition of the blood is directly toxicological, or a pathological result of stasis in the peripheral vessels. I incline to regard it as due to the latter condition, and I believe this explanation also holds good in the case of serpent poisoning.