STUDIES IN TEMPERATURE SENSATION. I. A COMPARISON OF THE SENSATION PRODUCED BY INFRA-RED AND VISIBLE RADIATION

Abstract

Few of the studies of temperature sensation have emphasized the importance of the perception of thermal change on the regulation of internal body temperature. Not only does the recognition of such changes make it possible for a man to provide a more comfortable environment for himself, but the automatic regulation of heat production and heat loss is dependent primarily upon it. The separate channels through which the human body dissipates its heat have been extensively studied and each of them has been shown to'be important under certain environmental conditions. The heat exchange between man and objects in his environment can be altered by increasing or decreasing the rate of blood flow to the skin. The resulting alteration of skin temperature varies the heat exchange by conduction, convection, vaporization, and radiation; and so balances the external heat loss against the heat produced by metabolism that a constant internal temperature is maintained. The recognition by the organism of the temperature of environmental objects is thus important for the regulation of body temperature. The temperature receptors in the skin which are responsible for the sensation of warmth and cold have been identified (1), and although these end organs are doubtless concerned in the autonomic control of skin temperature, there is no proof that other end organs may not be equally important. However, the study of temperature sensation is the most convenient way of investigating the perception of environmental temperature change. The knowledge of temperature sensation as it is ordinarily experienced is meagre because almost all experiments have been performed by placing hot or cold objects on the skin so that only the effect of conducted heat or cold has been determined. Such thermal stimulation is always combined with tactile sensation and is quite different 1 New York Hospital Research Fellow. from the stimulation produced by a change of environmental convection or radiation. These latter changes are experienced much more frequently than those due to contact with warm or cold bodies. There are many reasons why radiant heat is the most suitable stimulus for a study of temperature perception. It is the only thermal stimulus which can be applied without simultaneously provoking another sensation. The magnitude of the stimulus is readily controlled and measured, and the accompanying skin temperature elevation can be determined. The duration of the radiation and the size of the area to which it is applied are unlimited. The use of penetrating radiation has made it possible to produce different types of thermal gradient change during heating and has proved useful in establishing the mechanism by which the end organs in the skin are stimulated by heat. Using radiant heat we have investigated several aspects of temperature perception and have discussed them in the following three parts: Part I considers the absorption of radiation by the skin and the relative effectiveness of radiations of different wavelength on the stimulation of warm sensation. Part II deals with the thermal changes in the skin which are responsible for the sensation of warmth. Part III discusses the minimum sensitivity of the body to temperature change and the effect of the size of the irradiated area on the sensation produced, as it is influenced by the number of end organs stimulated and by spatial summation of the separate end organ responses. Of all forms of thermal stimuli, radiation is the most frequent and physiologically the most important. Changes in environmental radiation are constantly taking place and a radiation stimulus always precedes a conduction stimulus whenever there is a marked difference of temperature. Furthermore, recent studies (4) have shown that 517