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Abstract

The sensitivity of flies and locusts to halothane and N2O was investigated. In this paper we report experiments concerning the allover motor activity in the animal as a whole. In order to determine how the size of neurons comes into play under anesthesia we experimented with different but closely related species of flies differing very clearly in size. For the same reason we chose locusts of different developmental states and consequently different size. It came out that the larger insects are more sensitive to anesthetics than the smaller ones.

The results confirm one of Sherrington's (1906) conclusions, which says the axon which conducts spikes cannot be the most sensitive part of the neuron to anesthetic action. He ascribed the highest sensitivity to synapses; this, however, does not match with our results. In agreement with our experimental data is the new hypothesis that long dendrites or axonal endings conducting graded potentials are those parts of the CNS that exhibit the highest sensitivity to anesthetic action. Further confirmation of this hypothesis by more direct approaches has to be provided.