SENSATION. 333 



instantly communicate a feeling of acute pain. 

 The bones, in like manner, scarcely ever communi- 

 cate pain in the healthy state, except from the appli- 

 cation of a mechanical force which tends to fracture 

 them. 



In all animals provided with a nervous system, 

 those nerves which convey the impressions of touch, 

 are universally present in all classes ; and among 

 the lowest orders, they appear to constitute the sole 

 medium of communication with the external world. 

 As we rise in the scale of animals we find the 

 faculties of perception extending to a wider range ; 

 and many qualities, depending on the chemical 

 action of bodies, are rendered sensible, more espe- 

 cially those which belong to the substances em- 

 ployed as food. Hence arises the sense of taste, 

 which may be regarded as a new and more refined 

 species of touch. This difference in the nature of 

 the impressions to be conveyed, renders it neces- 

 sary that the structure of the nerves, or at least of 

 those parts of the nerves which are to receive the 

 impression, should be modified and adapted to this 

 particular mode of action. 



As the sphere of perception is enlarged, it is 

 made to comprehend, not merely those objects 

 which are actually in contact with the body, but 

 also those which are at a distance, and of the exist- 

 ence and properties of which it is highly important 

 that the animal, of whose sensitive faculties we are 

 examining the successive endowment, should be 

 apprized. It is more especially necessary that he 

 should acquire an accurate knowledge of the dis- 

 tances, situations, and motions of surrounding 

 objects. Nature has accordingly provided suitable 



