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A trace gas technique for measuring clothing microclimate air exchange rates. The rate at which clothing microclimate air is exchanged for ambient air influences the sensible and insensible heat loss from the microclimate. Factors which influence this air exchange are clothing permeability, wind speed, body movements, clothing design, and fabric properties. The influence of the first four factors has been studied using a trace gas technique for measuring the rate at which microclimate air is exchanged for ambient air. The trace gas technique and the mathematicalmodel describing the loss of the trace gas from the microclimate are described. The technique is shown to have a high resolving power, enabling small changes in the four factors studied to be identified, and as the method is also very quick detailed studies of garment design can be made.

SUMAARY1. The influence of repeatedly raising the body temperature by radiant heat to a level at which acclimatization to heat is normally acquired was investigated in two series of experiments, the first without the subjects sweating, the second with sweating.2. In a second investigation local sweat-gland activity was induced by drug injections on successive days without raising the body temperature.3. These experiments show that the increased sweating capacity characteristic of acclimatization to heat is a result of sweat-gland activity and does not appear to be induced by or to depend on an elevated body temperature.4. Secretory activity results in a loss of glycogen from sweat-gland cells on the first day of heat exposure but not after the glands have been 'trained' by acclimatization to heat.5. The state of acclimatization has no influence on the threshold concentration of acetylcholine required to elicit sweating when injected intradermally.

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The increase in blood flow produced by radiant heating of proximal areas of the forearm has been found to be associated with concurrent vasodilatation in the distal portion of the limb (Crockford & Hellon, 1959). This phenomenon is not dependent on central-nervous-system connexions since it occurs in subjects with complete brachial-plexus tears as well as in individuals with nerve blocks between the heated area and the spinal cord (Crockford, Hellon & Parkhouse, 1962). The centrifugal spread of the vasodilatation is prevented, however, by subcutaneous injection of either adrenaline or lignocaine immediately distal to the heated area. It was suggested on the basis of these studies that the spread of the vaso-dilatation may be conducted directly through the muscle walls of the subcutaneous arterial plexus. The present work attempts to determine whether the cutaneous erythema caused by rubefacients or by ultra-violet radiation is associated with changes in blood flow in the forearm similar to those produced by heating. METHODSLocal areas of erythema were produced on the forearm of three healthy male subjects by the application of either a 5 % cream or a 20 % aqueous-glycerine mixture of Trafuril (tetrahydro-furfuryl nicotinic acid ester, Ciba Laboratories, Ltd). This rubefacient was rapidly applied to an area 7 cm in width encircling the forearm just below the antecubital fossa. Within 5-10 min the rubefacient produced a sharply demarcated zone of bright erythema sometimes associated with sensations of mild burning and warmth. The cutaneous irritation subsided within a few hours after the material was washed off, and as a rule only slight erythema was visible on the following day. The effects of the rubefacient were also studied in three subjects with severe brachial plexus injuries. Each of them had paralysis of one arm with total sensory loss and muscle wasting. The site of the traction lesion was thought to be distal to the dorsal root ganglia, because of the absence of intradermal histamine flares and cold vasodilatation reactions (Bonney, 1959). The skin temperature of the denervated arm in each of these individuals was lower than that of the normal arm. Since the erythematous action of Trafuril is thought to be diminished by cooling of the skin surface (Nassim & Banner, 1952), warm air was carefully blown on the arm to relax the superficial vasoconstriction.

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