1. The study of insect curarization in the cockroach, Periplaneta americana, has been continued. The application of curare solution (0·032 M dTC) to the nerve cord produced blockage of action-potential conduction in the giant fibres lying within the nerve cord.

  2. The application of curare solution to the cerci prevented the recording of action potentials from the cereal nerves of the organism. Application of dTC to the cereal nerve-A6 region of the cockroach prevented giant fibres from responding to electrical stimulation of the cereal nerves. These results are interpreted as indicating that curare blocks the conduction of action potentials in the cereal nerve.

  3. It is proposed that curare can induce blockage of conduction in sensory, motor and central nervous system fibres. It is further proposed that this blockage of conduction is the mechanism of insect curarization.

  4. The results of previous reports concerned with insect curarization are re-interpreted in view of the proposal. Several of the conflicts in these reports are resolved by the proposal that blockage of conduction is the mechanism of insect curarization.

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