CUTANEOUS SENSATIONS 303 



by changes in the temperature of the skin, to a less extent 

 by constant high or low temperature. 



Under certain circumstances a paradoxical ^sensation of cold can 

 be produced by the application of a warm body to a cold point. 



The detection of differences in temperature is most delicate 

 when the objects coming in contact with the skin have a 

 temperature between 27 and 33. Between these tempera- 

 tures we are able to perceive a difference in temperature of 

 ^L- C. For the higher and lower temperatures the detec- 

 tion of differences is less accurate. 



The end-bulbs of Krause are probably the organs for the sensation 

 of cold ; the so-called genital corpuscles, for sensation of heat. 



(d) Sensation of pain. The pain points can be stimu- 

 lated by a great number of stimuli. The intensity of pressure 

 and temperature stimuli in order to produce a sensation of 

 pain must be greater than that necessary to produce sensa- 

 tions of touch and temperature. 



The sense organs for pain are probably the free nerve 

 endings in the epidermis. In the central part of the cornea, 

 where only pain points are present, only free nerve endings 

 are found. 



The sensation of pain appears and disappears more 

 slowly than tactile and temperature sensations. When the 

 stimulus is of short duration, it can be noticed that the sen- 

 sation of pain is preceded by a sensation of touch or tempera- 

 ture. When more than 20 stimuli per second are received, 

 we can no longer distinguish individual stimuli. 



3. The localization of sensation in the skin. Sense of 

 locality. The sensations produced by stimulation of the 

 skin are associated with conceptions of definite areas of the 

 skin. By this we are able to locate the place stimulated. 



The measure of this power of localization is the distance 

 that two parts of the skin must be separated in order that by 

 their stimulation two distinct sensations shall result. The 

 power of localization has thus far been determined chiefly for 

 the tactile sensation. 



The distance which these two points must be separated 



