628 PHYSIOLOGY 



skin is very cold or very hot the temperature sense is not nearly so delicate. 

 This sense presents the phenomenon of adaptation in a marked degree. 

 It is a familiar experience that, on coming from the external air on a cold day 

 into a warm room, a sensation of warmth is experienced all over the body. 

 In a few minutes this sensation wears off. On now leaving the room to go 

 outside again, the sensation of cold is at once appreciated, to disappear in its 

 turn after a few minutes. The effect of adaptation is still better shown by 

 the experiment of taking three basins of .water, a, b, and c ; a contains cold 

 water, b tepid water, c hot water. The left hand is immersed in the cold 

 water and the right hand in the hot water for a few minutes. On now placing 

 both hands into the basin of tepid water it feels hot to the left hand and cold 

 to the right hand. Such experiences as this led Weber to the conclusion 

 that the essential stimulus for the temperature sense was not the actual 

 temperature to which the sense organs were subjected, but the fact of a 

 change of temperature. He imagined that, while the temperature sense- 

 organs were being warmed, a sensation of warmth was produced, and when 

 their temperature was being lowered, a sensation of cold. Such a theory 

 would not however account for the fact that, above a certain tempera- 

 ture, water may feel warm and the feeling may continue so long as the skin 

 continues to be stimulated. On a cold day the air may feel cold to the face 

 and the feeling may last the whole time that the face is exposed. Moreover 

 we have in the temperature sense conditions which remind one of the after 

 images which occur in the eye. If a penny be pressed on the 

 forehead and then removed the sensation of cold lasts some little 

 time after the penny has been removed. In this case a sensation 

 of cold is produced although the end organs are being gradually 

 warmed up after the removal of the penny. In order to account 

 for these facts Hering, at a time when the differentiation of hot and cold 

 spots had not yet been effected, suggested that the temperature sense organs 

 could be regarded as having a zero point at which no sensation was produced. 

 If their temperature was raised above this point a sensation of warmth was 

 produced and vice versa. The zero point however was not a fixed one, but 

 could move upwards to a certain extent on prolonged exposure to high 

 temperature, or downwards on prolonged exposure to a low temperature. 

 In the light of the researches of Blix and Goldscheider we should have to 

 apply Bering's theory of a zero point to each of the temperature end organs 

 separately. 



A cold pencil passed over a warm spot evokes no sensation whatsoever. 

 If however a pencil considerably warmer than the skin be passed over a cold 

 spot, this may be excited so that the paradoxical result is produced of a 

 sensation of cold as the result of stimulation by a warm body. It is a 

 familiar fact that the immediate effect of entering a hot bath is very much 

 the same as that of entering a cold bath, viz. a rise of blood pressure and 

 contraction of the unstriated muscles of the skin and hair follicles with the 

 production of * goose skin.' It has been suggested that the distinctive 

 quality of a sensation of hoi as compared with that of warm is due to the 



