28 PHYSIOLOGY. 



the function of the nerves, more strictly so called, will, of course, 

 be sufficiently explained. 



CHAP. I. OF SENSATION. 



XXXVI. Our sensations may be considered as of two kinds: 

 1. Those which arise from the impulse or impression of external 

 bodies, which we therefore name SENSATIONS OF IMPRESSION. 

 " I perhaps am not very strict and accurate in the use of terms, 

 in saying from impulse and impression. To obviate this dif- 

 ficulty, I say that when I use the term impression, it applies 

 to all the several modes of giving or exciting motion." 2. 

 Those which arise from the minors being conscious of its own 

 action, and of the motions it excites ; and these we name SEN- 

 SATIONS OF CONSCIOUSNESS. 



- 



Sensations of Impression. 



X3tXVII. The sensations of impression are very various, 

 but have been generally referred to five heads or kinds, com- 

 monly called the five senses ; that is, those of sight, hearing, 

 smell, taste, and touch. 



XXXVIII. The first four of these are each of them proper- 

 ly considered as forming one genus of sensations : 1. As 

 the particular sensations comprehended under each head 

 (XXXVII.), though very various, are, however, perceived to 

 have somewhat common to all of them. 2. As those of the 

 same genus all arise from impressions made upon one part of 

 the body only, and that of a peculiar organization. 3. As 

 those of the same genus all arise from the action of external 

 bodies of one kind only, or of one and the same quality, by 

 means of which they act upon our organs. 



XXXIX. No such characters concur in establishing one 

 genus of the sensations referred to the fifth head of touch, 

 which are various in all those respects (XXXVIII.) ; and phy- 

 siologists seem to have referred, to this head of touch, every 

 sensation that does not manifestly belong to the other four ; 

 and, among the rest, many of the sensations of consciousness. 

 It might perhaps be useful to distinguish into genera the se- 



