FEELING AND TOUCH. 397 



another ; it is, however, commonly observed that the heat of 

 the body is best judged of by the lips, the cheeks, and the 

 back of the hand : a physician,who desires to ascertain the tem- 

 perature of a patient's skin, tries it with the back, not the 

 palm of the hand ; for the same reason, if we wish to discover 

 if some imperceptible drops of rain are falling, we put out the 

 back, not the palm of the hand. This sense of temperature 

 acts only through comparison ; it does not indicate the tem- 

 perature of the skin, but only the rise or fall of the temper- 

 ature; for instance, we are conscious of the difference in 

 temperature between our hand and forehead only at the 

 moment when we touch the forehead with the hand. 



In order to bring this thermal sensibility into play, the 

 temperature to be ascertained must be between and 70 

 (C.) ; outside of these extremes only painful sensations of 

 cold or heat are felt, and we are unable to judge of the 

 difference of a few degrees: we judge best of a slight varia- 

 tion in the temperature of a body when between 30 and 50 

 (C.) ; in other words, the temperature is more easily ascer- 

 tained the nearer it approaches that of our own body, and 

 also if a considerable part of its surface be compared at the 

 same time ; thus a finger dipped into a fluid at 37 (C.), gives 

 an idea of less heat than an entire hand in one at only 30 

 (C.). Anasrnia appears to increase the sensibility of the skin 

 to differences of temperature, while hyperaBinia diminishes it. 



The sensation of pressure, produced in us by different 

 bodies, is very unequally distributed in different parts : it is 

 most acute at the tip of the tongue and the ends of the 

 fingers: thus the digital extremities are points in which our 

 sense of touch chiefly lies. In order to decide exactly the 

 degree of sensitiveness of different parts of the body, a pair 

 of dividers is employed (Weber's compass), 1 and the degree 

 of sensibility of the surface is measured by the distance that 

 one leg of the dividers is from the other, when a person can 

 perceive the impression of the two points of contact ; the less 

 the distance between them, the greater the amount of sensi- 

 bility. At the tip of the tongue 1 m.m. of distance is suffi- 

 cient ; 2 m.m. on the palm ; and 12 in.m. on the back of the 

 hand : while on the skin of the trunk, especially in the dorsal 

 region, the distance must be 5 or 6 Centimetres. 



While applying the name of circle of sensation to that ex- 



1 See Weber, Art. " Tastsinn " in "Wagner's Handworter- 

 buch der Physiologic." 



