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The observation that in a group of substances derived from liquorice, anti-inflammatory activity as determined by the cotton pellet test seemed to be associated with irritant effects at the site of injection, led to the investigation of the effect of known irritant substances. It was found that tartar emetic, croton oil, talc and animal charcoal caused a significant reduction in the granulation tissue deposited around cotton pellets implanted in both intact and adrenalectomised rats. It is suggested that there is some limit to the total number of leucocytes which, in the course of a few days, can be mobilised to take part in an inflammatory reaction. Thus the two sites at which irritant effects have been produced, i.e. the site of implantation of the cotton pellets and the the site of injection of the irritant substance, compete for these cells, giving apparently an “anti-inflammatory” effect. This may well represent an important disadvantage of the cotton pellet test, making it suitable only for the investigation of non-irritant substances.