. The Biological bulletin. Biology; Zoology; Marine biology. TOXICITY OF DORID NUDIBRANCHS 295 way from a cannula in one carotid artery. Electrocardiograms were recorded simultaneously from Lead II. A dose of 100 mg dry substance per kg body weight was lethal in 20 min. Heart rate fell from 390 to 150 per min and systolic pressure from 120 to 35 mm Hg within a few seconds of the injection. In four other animals doses of 14 to 22 mg/kg decreased the heart rate by 72% and the systolic arterial pressure by 53% within 30 seconds of the injection. A representa- tive experiment is shown in Figure 2.
. The Biological bulletin. Biology; Zoology; Marine biology. TOXICITY OF DORID NUDIBRANCHS 295 way from a cannula in one carotid artery. Electrocardiograms were recorded simultaneously from Lead II. A dose of 100 mg dry substance per kg body weight was lethal in 20 min. Heart rate fell from 390 to 150 per min and systolic pressure from 120 to 35 mm Hg within a few seconds of the injection. In four other animals doses of 14 to 22 mg/kg decreased the heart rate by 72% and the systolic arterial pressure by 53% within 30 seconds of the injection. A representa- tive experiment is shown in Figure 2. The hypotension and bradycardia are remarkable for their long duration. Although no attempt was made to determine how long these effects lasted, they were still present for up to 60 min or when the experiments were terminated. The hypotension occurs without decrease in pulse pressure, suggesting that peripheral vasodilation is not involved in its production. The hypertension pro- duced by epinephrine (1 ) and norepinephrine (1 jug) were approximately the same after administration of the toxin as before, indicating that the arteriolar musculature responds to sympathomimetic substances and is not paralyzed by dorid toxin. Carotid sinus reflexes, activated by clamping the remaining patent artery, were still present during the profound hypotension produced by dorid toxin. This suggests that the substance does not block ganglia, since this reflex arc is functional. Effects of dorid toxin on isolated heart Dorid toxin produced ventricular standstill in the perfused isolated frog heart. It blocked contraction of the hearts of specimens of Mytilus californianus and Mereenaria niereeuaria in vitro, as well as that of the isolated spontaneously beating guinea pig atria. The effect on the latter heart preparation is shown in Figure 3. Dorid toxin has both negative chronotropic and inotropic effects in this preparation. Fifty per cent decrease in amplitude is produced by a concen- trat
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