442 HANDBOOK OF PHYSIOLOGY ^^ NEUROPHYSIOLOGY I 



TABLE 2. Threshold '] emperatiiri's Jul Warmth During Healing of Body in Climate Chamber* 



* Average values from 8 experiments [From Marechaux & Schafer (67).] 



by Goldscheider & Hahn (33) who showed that .sub- 

 cutaneous injections of saline of I3°C ehcited a dis- 

 tinct cold sensation while injections of 50°C saline 

 elicited a sensation of warmth, whereas according to 

 Ebbecke's view a sensation of warmth should have 

 been produced in both cases. 



From further experiments in which the tempera- 

 ture change and the change of the spatial gradient 

 ran in opposite directions, Hensel (42) concluded that 

 the intracutaneous temperature gradient or its tem- 

 poral change cannot be the decisive condition for the 

 production of a thermal sensation but the simple 

 warming or cooling of the receptors, independent of 

 the intracutaneous temperature gradient, is deter- 

 minative. Bazett & McGlone (4) also observed that 

 cooling from the lower surface of a double fold of the 

 skin of the prepuce led to a sensation of cold in the 

 upper surface. In their further investigations, carried 

 out to test the validity of Ebbecke's spatial gradient 

 hypothesis, they observed that sensations of intense 

 warmth or heat were found to be induced on release 

 of stasis in a limb maintained before, during and after 

 stasis in a bath at the blood temperature level, so that 

 on release no changes in temperature occurred and 

 no thermal gradient was established. This warm 

 sensation they attributed to a chemical stimulus 

 derived from metabolic processes particularlv in 

 muscle tissue by means of a substance that varies in 

 concentration both during asphyxia and as a result 

 of temperature changes in a manner similar to that 

 of acid. 



According to Lewis et al. (66) and Zotterman (95) 

 the sensation of tingling which occurs after the release 

 of the blood flow to limbs in which the circulation has 

 been arrested is attributable to an excitation of fibers 

 in the nerve trunk in the area of compression. The 

 sensation of tingling after release of the blood flow 

 can be greatly enhanced by hyperventilation and its 

 appearance can be entirely prevented by breathing 

 1 2 per cent carbon dioxide in oxygen (29). The sensa- 

 tion of warmth upon release has, however, a quite 

 different time course from that of tingling which 

 appears after a latency of 30 to 60 sec, and the sensa- 



tion of warmth which is immediately experienced 

 upon release is therefore most likely due to a stimula- 

 tion of the receptors in the periphery, as Bazett & 

 McGlone assumed. The only direct knowledge of the 

 influence of ischemia on thermal receptors comes 

 from Hensel (47) but is limited to the behavior of cold 

 receptors. He noticed that ischemia abolished within 

 a few minutes the steady discharge of the cold fibers. 

 Upon release of the blood flow the discharge immedi- 

 ately reappeared reaching the initial frequency within 

 15 to 30 sec. In the same way as the steady discharge 

 disappears during ischemia, the excitability of the 

 receptor to cold increases is gradually paralyzed. 



Although Lele et al. (65) repudiate "the spatial 

 intracutaneous gradient theory which is based upon 

 the assumed presence of specific encapsulated thermal 

 receptors" on anatomical as well as on physiological 

 grounds, they maintain that the thermal sensations 

 reported in the presence of an absolutely constant 

 surface skin temperature are due to a difference in 

 temperature between different strata of the skin in 

 which the terminals of the unencapsulated nerve 

 endings and their nerve trunk lie. They suggest that 

 the unencapsulated endings give rise to propagated 

 disturbances when a difference of temperature exists 

 between stem axons and terminals and that they are 

 so arranged that the skin l)ehaves as a thermopile 

 type of 'bolometer' rather than as 'thermometer'. 

 They believe that the anatomical arrangement of 

 these unencapsulated nerve terminals in the skin is 

 such that it is likely that different teinporospatial 

 patterns of action potentials will be evoked from the 

 same area of skin when the temperature is raised or 

 lowered. The patterns evoked will not be due to the 

 fact that certain receptors have specific properties not 

 possessed by others but due to the fact that numerous 

 nonspecific receptors are disposed in different strata 

 of the skin which are not at the same temperature. 

 They further maintain that these endings, which sub- 

 serve warm and cold sensibility can, if stimulated in 

 the appropriate way, give rise to other sensations not 

 associated with the thermal modality such as touch, 

 prick, itch and sharp pain. 



