CUTANEOUS^SENSATIONS 545 



temperature, or downwards on prolonged exposure to a low tempera- 

 ture. In the light of the researches of Blix and Goldscheider we should 

 have to apply Hering's theory of a zero-point to each of the tempera- 

 ture end-organs separately. 



A cold pencil passed over a warm spot evokes no sensation what- 

 soever. 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 

 with 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 un- 

 striated 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 hot as compared with that of warm is due to the simul- 

 taneous stimulation of warm spots and cold spots. When testing the 

 distribution of the temperature sense it is found that the sense of cold 

 is evoked more promptly than that of warmth. This is interpreted 

 as showing that the end-organs for the warm sense are situated more 

 deeply than those for cold. We have no evidence as to the histological 

 identity of these organs. 



THE SENSE OF TOUCH 



By means of the sense of touch we arrive at a conclusion as to the 

 qualities, such as shape, texture, hardness, &c., of the bodies with 

 which the skin is in contact. In this judgment, however, very many 

 other sensations are involved besides those which can be regarded as 

 strictly tactile. Thus the hardness of an object signifies its resistance 

 to deformation, besides its power of deforming the skin surface with 

 which it is in contact ; the former quality, i.e. of resistance, is one 

 which involves the muscular sense, since we judge of it by the extent 

 to which we can move our muscles without causing any alteration of 

 the surface of the body. 



The tactile sensibility of the skin as a whole, like its temperature 

 sensibility, is due to the presence in it of a number of touch spots, 

 i.e. small areas which are extremely sensitive, separated by areas 

 almost or entirely insensitive to pressure. The tactile sensibility of 

 any part is proportional to the number of such touch spots present. 

 If the calf of the leg be shaved .and then tested by pressing on it with 

 a fine bristle or hair it will be found that the minimal stimulation 

 used evokes sensation only at certain definite points, the * touch spots/ 

 In a square centimetre of such skin there may be about fifteen touch 

 spots. On thrusting a fine needle into one of these spots a sharply 

 localised sensation of pressure is produced unaccompanied by any 

 painful quality and often described as having a ' shotty ' character, 



35 



