These drugs are supposed to act upon the heat regulating centre of the body, throwing it out of function, the heat then accumulating in the body as it is formed by oxidation and other processes, until, by a diffuse dilatation of the blood-vessels, the body loses a large amount of heat, even chills and rigors with possibly sweating and collapse resulting. Large doses of these drugs "lake" the blood, break up the red blood cells, and form methaemoglobin. Cf. Potassium Chlorate, p. 42. The cyanosis may be caused partly by this, partly by the dilated blood-vessels, and partly by the weak circulation due to collapse. The drugs so acting are antipyrine, acetanilide, resorcinol, and phenacetine.