The chemical irritants o-chlorobenzylidene malononitrile (CS), n-nonanoylvanillylamine (VAN) and dibenzoxazepine (CR) and several of its derivatives have been assayed using the human blister base. The relative potencies found by this method, CR greater than VAN greater than CS, conflicted with those found in non-human test systems but the rank order of potency of CS and CR reflected that reported in tests on the human eye and tongue. Data derived from humans thus appear to be of importance when assessing irritant potency. Interactions between CS, CR, VAN, capsaicin and bradykinin were investigated to discover any common pathways of irritant activity. Self-desensitization developed on repeated application of all agents to the blister base and selective cross-desensitization also occurred.

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The effects of chemical irritants on the membrane potential and input resistance of the giant amoeba, Chaos carolinense, have been investigated. The membrane potential and input resistance were −111.5 mV and 8.6 MΩ respectively In the resting state the cell membrane of Chaos carolinense was found to be impermeable to Na+ but permeable to K+. The distribution of K+ across the cell membrane conformed to a Donnan equilibrium with the resting membrane potential being the K+ equilibrium potential The chemical irritants dibenzoxazepine and its 2‐chloro‐ and 3‐chloro‐analogues and o‐chlorobenzylidene malononitrile produced a fall in input resistance but no change in membrane potential. It is suggested that these effects are caused by an increase in K+ permeability The potencies of a series of chemical irritants with respect to dibenzoxazepine were measured on the giant amoeba. These potencies did not reflect those found in mammalian preparations.