. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Tevtperature: Metabolic Aspects and Perception 365 summation occurs, in that the threshold for stimulation of large areas is less than that for stimulation of single sensory endings, an area of cold receptors being stimulated by a fall of °/sec., and one of warmth receptors by a rise of °/sec. for 3 seconds.'- Non-penetrating infrared is more effective as a thermal stimulus than are penetrating rays; therefore the thermal sense appears to depend more on the thermal gradient in the skin than on absolut
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Tevtperature: Metabolic Aspects and Perception 365 summation occurs, in that the threshold for stimulation of large areas is less than that for stimulation of single sensory endings, an area of cold receptors being stimulated by a fall of °/sec., and one of warmth receptors by a rise of °/sec. for 3 seconds.'- Non-penetrating infrared is more effective as a thermal stimulus than are penetrating rays; therefore the thermal sense appears to depend more on the thermal gradient in the skin than on absolute tempera- ture or even rate of change of temperature in the skin.'-'-* It is also possible to obtain pain with thermal stimulation, but the skin receptors are not the same, llo loo - AIR. — DEGREES CENTIGRADE lo 15 20 25 30 35 40. 40 5o 60 70 60 90 loo AIR TEMPERATURE — DEGREES FAHRENHEIT Fig. 95. Body temperature of wrens at different air temperatures at different ages after hatching. From ;* as shown by the following: the pain threshold is raised and the heat threshold lowered by acetylsalicylic acid; after occluding tbe blood flow to an arm for some minutes only the pain sense remains, and pain shows little summation as compared with heat or cold.^^ The-threshold for pain by a 3-minute thermal stimulation is , compared with the warmth threshold of ''^- The nervous pathways by which reflex responses to thermostimulation are elicited are not well known. There may be local vascular reactions, largely by axon reflexes, also some direct responses of blood vessels to temperature change, but the principal responses of vasodilation, vasoconstriction, and hair. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prosser, C. Ladd (Clifford L
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