The human body exhibits little or no response to contact with the tentacles of specimens of Cyanea capillata from Chesapeake Bay. 2. Three types of nematocysts were identified: atrichous isorhizas, holotrichous isorhizas, and heterotrichous microbasic euryteles. 3. The tubes of nematocysts discharged into 2% agar take a sinuous course, often coiling on themselves. Most tubes penetrated less than 350µ. 4. Although faradic shock and FAA caused discharge of nematocysts from living tentacles, they failed to produce discharge of isolated nematocysts. 5. Homogenization of thoroughly washed frozen nematocysts causes rupture, releasing the toxic principle which is a single protein. 6. The LD 50 of the toxin was of the order of magnitude of µg/g of mouse body weight. 7. Mice were unaffected by intraperitoneal injections of washed capsular debris and tubes, or lipids, or of washed undischarged nematocysts in moderately heavy suspensions.
