THE SENSATIONS OF TEMPERATURE, PAIN, AND PRESSURE

Abstract

The graphs for the four kinds of cutaneous sensations discussed above are all of the same type, consisting in their entirety of at least two branches. These correspond exactly to the first and second branches of the graphs obtained for the tactile sensations by Allen and Weinberg (3). Probably if the measurements could have been extended over greater ranges of current‐intensities a third branch would have been found, as in the senses of vision, touch, and taste. The graphs all conform to the same equation found for the sense of touch:D=—k log I+ C.The order of magnitude of the times of duration of the stimulus at the critical frequency of stimulation is also the same for all the sensations discussed in this paper, and for touch. We may conclude, therefore, that all the cutaneous sensations obey the same fundamental laws. In the equations to the graphs the constants k and C have different values for the two, or more, branches, and they are different for the different sensations. The negative sign for k indicates that the duration of the stimulus at the critical frequency of stimulation diminishes as the intensity of the stimulus increases.The measurements obtained in these investigations, as far as we can judge, are the normal values for the receptors indicated. No measurements under the conditions of depression and enhancement of sensitivity seemed possible, as there was no certainty that the same receptors were stimulated on different occasions. There can be no doubt, however, that both processes are in operation in all these sensations. The interpretation of the two‐branched graphs most probably rests upon the functions of the sensory reflex actions involved. In other researches on the sensations of vision, touch, and taste, experiment justified the conclusion that in each sense reflex actions of two kinds existed, one of which depressed and the other enhanced the sensitiveness of the receptors. It is a sudden change in the ratio of these two processes that causes a corresponding alteration of the sensitivity of the receptors and thereby of the slope of the graph.In the sense of touch it was found that stimulation of low intensities corresponding to the uppermost branch of the graph elicited enhancement in excess of depression, while higher intensities of stimulation caused the reverse. Since the other cutaneous sensations are found to conform to the same equation, it may be inferred that the results of stimulation will also be similar. Experience under pathological conditions also testifies to the existence of enhancement and depression of receptor sensitivity in the senses of temperature and pain.This investigation is one of a series of researches relating to colour‐vision and other sensory actions now being conducted under the direction of Professor Frank Allen, with the financial assistance of the National Research Council of Canada, to which body we desire to express our thanks.