1. In the cases of fever investigated the flow in the feet never exceeded the normal flow and was usually much below the normal 2. In explanation of the relatively small foot flow in the fever cases it is suggested that the vasoconstrictor mechanism of the peripheral parts, especially of the skin, is abnormally excited, and some direct evidence that this is the case is brought forward. 3. The significance of this hypersensitiveness, or at least increased action, of the cutaneous vasoconstrictor mechanism is assumed to be that the peripheral vasoconstriction is a compensatory arrangement which secures for the organs mainly suffering from the infective process an increased flow of blood. 4. On this hypothesis the rise of temperature is, chiefly at least, secondary, inevitably following the vasoconstriction, provided that the metabolism is, upon the whole, not diminished. 5. Accordingly the rational treatment of hyperpyrexia, or of pyrexia if it is considered necessary to treat it, is to abstract heat by a process which will not diminish and may even increase the cutaneous vasoconstriction. This condition is exactly fulfilled by the cold bath, at least as regards its initial effect. Other so called tonic effects of the cold bath are not considered here. Antipyretic drugs which act by dilating the cutaneous vessels would seem to be inferior in this regard. They diminish the temperature, it is true, but at the cost of defeating the beneficial redistribution of the blood which it is the function of the peripheral vasoconstriction to insure. 6. It is obvious that for the elimination of a given quantity of heat from the skin by radiation and conduction in fever, a smaller cutaneous blood flow will suffice than with normal body temperature, since the elimination of heat per gram of blood passing through the surface must be greater in fever owing to the greater difference of temperature between the surface of the body and its surroundings. I am much indebted to the staff of the City Hospital for their coöperation which has rendered this investigation possible.