220 THE HUMAN BODY. 



if they are placed on the same side of the body. If two 

 points are" touched, which are subject to variation from func- 

 tional displacement, the eyelids. or the lips for example j the 

 distance is greater than if the two contacts take place on one 

 eyelid, or one lip. This sense is also increasingly developed 

 on the surface of the limbs in proportion to the distance 

 from the body. 



The sensation of contact varies according as it results from 

 a simple application of a foreign body to the skin, or from a 

 shock, or a succession of shocks repeated at short intervals, 

 like that which produces vibration in a body. In the latter 

 case the region of contact receives a shock in proportion 

 to the intensity of the vibrations; as when we touch the skin 

 with a timing instrument while vibrating, or if we grasp a 

 vibrating metallic body or wooden rod, or close the lips 

 against the reed of a basoon while it is being blown into, it 

 produces on the surface in contact an impression, varying 

 from a painful shock to a simple tickling or pleasurable sen- 

 sation. It is a sensation of the same nature, though diffused 

 through the whole body, that we feel from the vibrations im- 

 pressed on the atmosphere by the explosion of artillery, the 

 roll of thunder, or the ringing of a great bell. The sense of 

 touch then gives us an idea of the sonorous waves which 

 excite the auditory nerve, and furnishes us with the proof, 

 that the same cause acts differently on the special nerves of 

 the different senses. In fact, the nervous papillae of touch 

 transmit a sensation of motion and of shock; the tympanum 

 perceives neither tickling nor shock, the impression which it 

 transmits to the auditory nerve is not that of a vibratory 

 movement, but of the sound which results from it. 



The sensation of pressure is distinctly perceived by touch; 

 but we must distinguish between the pressure of a body 

 against the skin, and the resistance which this body offers to 

 a muscular effort tending to displace it. If when the hand 

 is supported, and a weight placed in it, no effort is made to 

 raise it, and the muscles remain inactive, we feel a sensation 

 of pressure, the force of which may be judged of with more 

 or less exactness; but the moment we endeavour to appre- 

 ciate the weight the sensation becomes complex, and we 



