94 PRODUCTION, &c. SECT. XIV. 9. 



life, owing perhaps to fome change which thefe animals have 

 undergone in the gradual progreflion of the formation of the 

 earth, and of all that it inhabit. 



Thefe feven laft mentioned fenfes may properly he termed 

 appetites, as they differ irom thofe of touch, fight, hearing, tafte, 

 and fmell, in this refpeft ; that they are affected with pain as 

 well by the defetl of their objects as by the excefs of them, 

 which is not fo in the latter. Thus cold and hunger give us 

 pain, as well as an excefs of heat or fatiety ; but it is not fo 

 with darknefs and filence, 



IX. Before we conclude this Se&ion on the organs of fenfe, 

 we muft obferve, that, as far as we know, there are many more 

 fenfes than have been here mentioned, as every gland feems to 

 be influenced to feparate from the blood, or to abforb from the 

 cavities of the body, or from the atmofphcre, its appropriated 

 fluid, by the ftimulus of that fluid on the living gland ; and not 

 by mechanical capillary abforption, nor by chemical affinity. 

 Hence it appears, that each of thefe glands muft have a peculiar 

 organ to receive thefe irritations, but as thefe irritations are not 

 fucceeded by fenfation, they have not acquired the names of 

 fenfes. 



However when thefe glands are excited into motions ftronger 

 than ufual, either by the acrimony of their fluids, or by their 

 own irritability being much increased, then the fenfation of pain 

 is produced in them as in all the other fenfes of the body ; and 

 thefe pains are all of different kinds, and hence the glands at 

 this time really become each a different organ of fenfe, though 

 thefe different kinds of pain have acquired no names. 



Thus a great excefs of light does not give the idea of light but 

 of pain ; as in forcibly opening the eye when it is much infla- 

 med. The great excefs of preffure or diftention, as when the 

 point of a pin is preffed upon our Ikin, produces pain, (and when 

 this pain of the fenle of detention is {lighter, it is termed itch- 

 ing, or tickling), without any idea of folidity or of figure : an 

 excefs of heat produces fmarting, of coid another kind of pain ; 

 It is probable by this fenfe of heat the pain produced by cauftic 

 bodies is perceived, and of ele&ricity, as all thefe are fluids, that 

 permeate, diftend, or decompofe the parts that feel them. 



SECT 



