The Effects of Diphtheria Toxin on the Cecropia Silkworm* by A. M. Pappenheimer, Jr., and Carroll

Studies on the metabolism of Corynebacterium diphtheriae have furnished evidence that diphtheria toxin is closely related to the protein moiety of diphtherial cytochrome b (8). These observations, in turn, have suggested the possibility that diphtheria toxin may exert its injurious action on the tissues of susceptible animals by interfering in some way with the normal functioning of the cytochrome system--perhaps by blocking the synthesis of cytochrome b or related components (7). Efforts to test this hypothesis have unfortunately proved inconclusive. Though changes in succinoxidase activity have been observed after injecting the toxin into pigeons, guinea pigs, and rabbits, the deviations, for the most part, have been relatively small and unconvincing. In the present investigation we have approached the matter from a new direction by a study of the effects of diphtheria toxin on the Cecropia silkworm--an insect which, for reasons which we may now consider, seems particularly suited for an analysis of this problem. Six weeks after hatching from the egg, the mature Cecropia caterpillar spins a silken cocoon within which it transforms into a pupa. Morphogenesis then comes to a standstill and the insect persists for 6 to 12 months in a state of dormancy, the pupal diapanse. Previous studies (14--20) have demonstrated an endocrine basis for the genesis and termination of diapause. Its onset apparently results from a prolonged delay on the part of the brain in secreting a hormone required for the initiation of adult development. Surgical removal of the pupal brain therefore stabilizes the animal in a state of permanent diapause. But under normal circumstances the pupal brain, activated by the low temperatures of winter, regains its endocrine powers and, by secreting its hormone, functions to terminate diapause the following spring. Adult development then proceeds promptly so that, at a temperature of 25°C., the adult moth emerges 21 days later.