272 RELATIVE NATURE OF SENSATION. 



an infant they are just as apparent as the phenomena to which 

 .we, in later life, learn to attach meaning and significance. 



The Relative Nature of Sensations. If one hand be 

 held in a basin of hot water and the other in a basin of cold 

 water, and then the two be suddenly plunged into a third 

 basin containing tepid water, a sensation of cold will be re- 

 ceived from the hand that was in the hot water, while the 

 hand from the cold water will feel heat. Sensations depend 

 on comparison and contrast. After listening to low sounds, a 

 sudden loud noise is painful ; and after hearing loud noises, 

 it is difficult to detect slight sounds. We hardly notice the 

 gradual fading of the light at sunset. And the nose does not 

 usually detect the slow fouling of the air in a room ; but let 

 one come in from the fresh outside air, and the contrast is 

 striking. A constant current of electricity usually causes a 

 muscular contraction at the time the current enters the muscle 

 and at the time when the current is stopped, that is, at the 

 " making " and the " breaking" of the current; but the muscle 

 ordinarily remains inactive while the current is passing. The 

 Interrupted Current, or Induction Current, is therefore com- 

 monly employed as a stimulus in physiological experiment. A 

 sudden change seems to be requisite for producing the nerve 

 impulse necessary to rouse a sensation in ordinary circum- 

 stances. Pressure may be applied so gradually that we fail 

 to notice it. The art of the pickpocket, of the ventriloquist, 

 of the sleight-of-hand performer, depends largely on this fact. 

 Attention is called to something else, and the work is either 

 quickly done when attention is completely absorbed on some- 

 thing else, or the act is so gradual that no sudden change is 

 noted. In smelling it is often necessary to sniff ; the sudden 

 rush of particles of air bearing the odorous particles against 

 the surface bearing the nerve endings seems to be necessary. 

 Perhaps this is why the fish has two nasal openings on each 



