738 



SPECIAL SOMATIC AND VISCERAL RECEPTORS 



is said to contain about 15 of these tactile receptors.^ The succeed- 

 ing table shows how great a pressure must be brought to bear upon 

 different regions of the skin in order to evoke minimal sensations ; the 

 degree of pressure being indicated here in grams per square millimeter 

 of area: 



• » • • • • 



• * • . • • 



111 



:•::: 



Fig. 368. — Cold and Hot Spots from the Anterior Surface of the Forearm. 

 a, Cold spots, b, Hot spots. The dark parts are the most sensitive, the hatched 

 the medium, the dotted the feebly, and the vacant spaces the non-sensitive. (Landois 

 and Stirling.) 



Tongue and nose 2 



Lips 2.5 



Finger-tip and forehead 3 



Back of the finger 5 



Palm of the hand, arm and thigh 7 



Forearm 8 



Back of the hand 12 



Back of the leg and shoulder 16 



Abdomen 26 



Sole of the foot 28 



Back of the forearm 33 



Gluteal region 48 



The acuity of the discriminating sense also varies in different regions of the 

 skin, as may be gathered from the succeeding table : 



Tip of tongue 1.1 mm. 



Palm of the last phalanx of the finger 2.2 mm. 



Palm of the second phalanx of the finger 4.4 mm. 



Tip of the nose 6.6 mm. 



Back of the second phalanx 11.1 mm. 



Back of the hand 29.8 mm. 



Forearm 39 . 6 mm. 



Sternum 44 . mm. 



Region along spine 54 . mm. 



Middle of the back 67 . mm. 



* Vitreg, Ber. der sachs. Gesellsch. der Wissensch., xxiii, 1896, and Kiesow, 

 Wundt's phil. Studien, xix, 1902. 



