72 THE FOUNDATIONS OF SCIENCE 



of fine hairs mounted on wooden handles. The 

 pressure which each hair is capable of exerting is 

 measured on a balance, and thus local differences 

 in sensibility may be mapped out. Again, by ex- 

 ploring the skin with blunt-pointed rods, either hot 

 or cold, the sensitiveness to heat and cold may be 

 determined. It is found that some areas are more 

 sensitive than others to each kind of stimulus, the 

 " touch spots " not coinciding either with the " heat 

 spots " or the " cold spots," and none of these being 

 coincident with the " pain spots," where painful 

 pressure is most easily felt. 



If a nerve connected with a given sensory area of 

 the skin be cut, the sensations are destroyed, and 

 only return slowly as the injury is restored. The 

 sensibility to pain returns first, and the feeling of 

 cold before that of heat. 



Thus we see that the extent to which the mind is 

 influenced by effects of pressure or of temperature 

 on the skin, does not depend alone on these outside 

 variables. The properties of the portion of the body 

 which is acting as receiving agent have to be taken 

 into account. 



The sensation of sight, like those of touch and 

 hearing, is one which is possessed alike by mankind 

 and the upper members of the animal world ; though 

 the range of the sensations probably does not corre- 

 spond in the various instances. 



