EFFECTS OF EXTREME HEAT.
The application of moderate heat to the surface of the body causes dilatation of the cutaneous capillaries. In such application the exhalant and perspiratory function of the skin is increased, by which means a rise in general body temperature is prevented. If, however, severe physical exertion accompany the exposure, a more pronounced result is induced and a depressing effect upon the nervous system becomes manifest. If the degree of heat be raised and the exertion increased and prolonged, marked depression ensues. Under circumstances of quiet and rest a high degree of temperature is borne by man without depression or discomfort, but with continued and severe muscular effort the rise in animal temperature is productive of distress and depressing conditions. In the Turkish or Russian baths, in the healthy subject, a temperature of 48.8° to 54.4° C. (120° to 130° F.) produces profuse perspiration but no depression, and a plunge in or affusion of cold water is not only borne with impunity but is acceptable. In conditions of heat accompanied by physical exhaustion, such sudden exposure to cold would prove extremely dangerous.
In the condition of rest, exposed to external heat, the tendency to elevation of body temperature arises from the external causes alone, which in no way specially modify the nutritive functions. But in the second condition the internal processes of nutrition, which have been subject to great stimulation, are suddenly embarrassed by suppression of the compensating activity of the cutaneous surface, and severe organic and nervous derangements follow.
In the summer season the temperature rises to 32.3° C. (90° F.) and even much higher in certain localities. During the prevalence of such heat, the mortality among young children, the aged and enfeebled is very marked; these two periods of life being very susceptible to the depressing effects of heat. A high temperature is easily borne if the air be pure and the atmosphere be not saturated with moisture. Telluric electric conditions also have a modifying influence, undoubted though obscure.
In certain occupations an intensely heated atmosphere is endured with impunity for a considerable time, provided the air be maintained in a condition of purity and water be supplied to the person exposed. The stokers upon ocean steam-ships, where a forced draught is employed, are subjected to extreme heat, sometimes reaching 60° C. (140° F.). Resort to forced and continuous ventilation of the stoke-rooms, with short hours of duty, renders tolerance of the high temperatures possible.