950 CUTANEOUS SENSATIONS. 



fauces and part of the pharynx, but not from the alimentary canal farther 

 down. When hot fluids are drunk, a sensation is obtained which is referred 

 to the pit of the stomach. E. H. Weber taught that this sensation has no 

 quality of "warmth," but is obscurely painful; but Schlesinger gives 

 distinct evidence to the contrary. 1 A clyster introduced per anum evokes 

 no sensation of cold until it is discharged, when, if at 15° C, it elicits 

 a strong sensation of cold from the anal skin. 2 I once had opportunity to 

 test the mucous membrane of the caecum for sensibility to cold and warmth. 

 I used small test-tubes containing water warmed (up to 50° C. at highest), 

 and cooled (at lowest, to temperature of melting ice). The patient experienced 

 no sensation whatever from any of them. 3 I also have had opportunity to 

 examine the small intestine by its peritoneal surface, also the surface of the 

 liver in the same way; in neither case did the patient experience any sensation 

 whatsoever. When very cold air is inspired through the nose, the sensation of 

 cold evoked is confined to the nostril, the floor of the nasal chamber, and the 

 upper surface of the soft palate. 4 In the hotter rooms of a Turkish bath, the 

 feeling of heat which is so marked at the nostrils is very slight inside the 

 nasal chamber; similarly, the very hot air does not cause lachrymation, 

 although very cold air easily does so. From the granulating surfaces of 

 wounds and cutaneous cicatrices thermal stimuli evoke no sensations of either 

 cold or warmth, although, if strong, they may produce sensations of pain. 5 



The adequate stimulus — In the cutaneous sensations of cold and 

 of warmth is exemplified with especial distinctness the physiological 

 law, that in the nervous system and its immediate agents, change of 

 condition, rather than absolute condition, acts as stimulus. The 

 warmth of the skin excites specific sensations chiefly when it undergoes 

 alteration. When a point of skin becomes cooler, then does it provoke a 

 thermal sensation. So long as its temperature remains unaltered, it does 

 not, except under extreme conditions, generate any thermal sensations. 



Under ordinary circumstances, a continuous stream of heat of fairly 

 steady intensity passes from the interior of the body outward through 

 the skin. So long as the conditions for this flow remain constant, the 

 temperature of end-organs in the skin also remains constant, and 

 different though the temperature of the different thermal end-organs in 

 different skin regions may be, no difference between them is felt. 

 The stream of heat flowing outward through the skin may be altered 

 by alteration of conditions either within or without. To take the 

 latter case first : the heat-stream may be checked by covering 

 the free surface of the skin with clothes ; the temperature of the 

 thermal organs in the clothed skin will then rise, and the skin 

 there will "feel warm," although the clothes are no warmer than 

 the skin was. On the other hand, the loss of the heat streaming 

 from the skin may be increased by simply cooling, without other- 

 wise altering, the surrounding medium. The temperature of the 

 thermal end-organs will then fall, and they will produce sensation of 

 cold. The heat-stream flowing through the skin will be influenced not 



1 Weber described the sensation evoked from the stomach by very cold fluid as possessing 

 slightly the quality of "cold," Wagner's " Handworterbuch, Bd. iii., Schlesinger, "Die 

 Syringomyelic," Wien, 1895, S. 23. 



"-' Weber found that if the clyster were quite cold and retained for a time, a sensation of 

 coolness is felt in the anterior abdominal wall ; he supposed this due to actual cooling of 

 the skin of the abdomen, ibid. 



3 Weber touched the mucosa of the sigmoid flexure with a hot iron through an artificial 

 anus ; no sensation was perceived, ibid. 



4 Weber, loc. cit. 



5 Cf. Weber, loc. cit., and others ; see Goldscheidcr, " Ueber den Schmerz," Berlin, 1894. 



