Studies with human volunteers have shown that animal experiments can seriously underestimate the likely effect of riot control gases on the eye. The tests found that people are 18 times more sensitive to CS than rabbits, and 90 times more sensitive to another sensory irritant, CR.(1)
When applied to the rabbit's eye, a solution of CR produced only "minor transient changes" in pressure within the eye. But instillation of a smaller amount into the human eye produced a 40% rise in pressure within 5 minutes compared with only a 3% rise after 10 minutes in rabbits.(2)
Species differences have also been found when CS and CR are applied to the skin. A method known as the human blister-base technique allows volunteers to classify irritants according to the level of discomfort they produce. The procedure showed that CR is a more potent irritant than CS which is confirmed by other human test systems, yet is the reverse of that found from experiments on rodents.(3) The study also found that a further sensory irritant,VAN, is less potent than CR which is again the opposite of that found from animal tests. In a masterpiece of understatement, the researchers conclude that "data derived from humans thus appears to be of importance when assessing irritant potency."(3)
1) D.W.Swanston in Animals & Alternatives in Toxicity Testing, Eds. M.Balls et al (Academic Press 1983).
2) B.Ballantyne et al in Current Approaches in Toxicology, Ed. B.Ballantyne (Wright & Sons, 1977).
3) R.W.Foster et al, Pain, 1986, vol.25, 269-278.
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