254 THE HUMAN SPECIES 



the forehead, temples, eyelids, back of the forearm and hand. 

 According to Weber, upon the most sensitive areas a man can 

 discriminate between weights in the ratio of 29 to 30. Dr. 

 Rivers found the tactile and pressure senses better developed 

 in the Papuans than in Europeans. 



No observations have been made on the temperature sense 

 in animals, although they must certainly be credited with per- 

 ceptions of heat and cold. 



In man the temperature sense is distributed over the whole 

 external skin, in the skin of external ear, the mucous membrane 

 of the mouth and throat, the anterior surface of the arch of the 

 palate, in the anterior nares and the floor of the nostrils, and 

 in the mucous membrane of the posterior nares. Physiologi- 

 cally, definite areas for heat and cold can be distinguished in 

 the skin ; 1 the latter are much more numerous and lie much 

 closer together than the former ; the number of heat-points is 

 only about 30,00x3, while there are some 250,000 cold-points in 

 the adult man. In consequence the sense of cold is much 

 more extensive and intense than that of heat. The less 

 numerous heat-points lie deeper in the skin, so that the hot 

 stimulus must be relatively greater to evoke the sensation of 

 warmth. Between the groups of heat- and cold-points there 

 are gaps about the size of a square centimetre where both 

 varieties are absent. Man calls those bodies cold which take 

 away the heat from the cold-points in the skin, and other bodies 

 hot which add to the heat of the heat-points. Various parts 

 of the skin interpret different degrees of heat unequally, and 

 the greater the difference in the thickness of the epidermis so 

 much the more obvious are the variations in the sensibility of 

 the part. In man the areas of extreme tactile sensibility coin- 

 cide with the areas of most delicate temperature sensation. 



The temperature sense is infinitely valuable to the life both 

 of man and beast, for it serves to warn against the extremes 

 of heat and cold. 



Popular journals and natural histories, both old and new, 

 make much of a so-called sense of direction as a most marvellous 

 sixth sense in animals. In text-books of comparative phy- 



1 Munk-Schultz, loc. cit., pp. 533-42. 



