Abstract
1. The pharmacological effects of neural transmitter and synephrine are compared with respect to induction of luminescence in extirpated larval firefly lanterns. 2. Transmitter and synephrine show many similarities of action. They are as follows: (a) They both act directly on the lantern. (b) Their response latencies are relatively constant. (c) Both stimulate ATP production. (d) Neither induces a persistent intermediate in anoxic lanterns. (e) No monoamine oxidase enzyme appears to act on them. (f) The luminescence-inducing action of both is rapidly blocked by chlorpromazine. (g) They show identical responses in the presence of dichloroisoproterenol. 3. Luminescence induced by transmitter is much more rapidly extinguished than that induced by syneprine. 4. The possible reasons for the difference in luminescence extinction rate between the two agents are discussed and their different modes of delivery are emphasized.

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