SENSE OP SMELL IN PISHES. 347 



respiratory organ in animals that live in the air, we hare 



some means of proving chemically the material existence of Proof*; of their 



those smells, the nature of which is best hnown. Thus the "^^^^,^'^'^^- 



exhalations from nitrous gas, volatile oils, and ether, for 



example, may be destroyed by the combination of some of 



their principles with oxigen ; and muriatic acid gas renders 



sensible to the eye the particles of ammonia, which cease 



to be odorate the moment this acid combines with them in 



the open air. 



The most perfect animals, those that possess all the five Senses of per- 

 scnscs, are so organized as to perceive the principal modifi- ^ctammas. 

 cations of the bodies surrounding them. They have sight, 

 to enjoy the effects of light; feeling, to appreciate the soli- 

 dity of palpable objects ; hearing, to distinguish the vibra- 

 tions of elastic bodies; taste, to discriminate the qualities 

 of bodies capable of becoming liquid; and lastly smeJl, to 

 collect the emanations of substances, that have the proper- 

 tics of a gas. 



Light exerts its action only on the eye ; not on the tongue, Each sense has 

 postrils, ears, or skin. It is the same with most smells, jg^t, 

 which do not act on the sight, taste, hearing, or touch. 

 Each of the organs of sense then has its particular function, dependent on 

 jSxed and determined beforehand by the arrangement of its^ e organ, 

 apparatus i for the sentient principle appears to be ideuti- as the sentient 

 cal, and placed, as we may say, on the watch on the inside ^'""^'P ®^''*** 

 of each instrument, in order to collect and transmit the 

 slightest modifications in the qualities of bodies. ^ 



The sensations of smell and taste however, are most ana- Smell and taste 

 Jogous, both in respect to the mode of action on our bodies, ^7^^°a"loer' 

 and to the apparent end at least for which nature seems to 

 have given us organs to perceive them. The odorate and 

 sapid particles are conveyed either by the airs that serve for 

 respiration, or the solid and liquid aliment that must enter 

 the stomach. Stopped on their passage through the nostrils 

 or the mouth, these particles touch the nerves distributed 

 on those parts, and thus give notice of their presence. The 

 jierve^ immediately excite the ideas of the sensations they 

 perceive, and excite us to admit or reject the air or food, 

 according as the impression produced on the organ is agreea- 

 ])le or not. The sapid and odorate qualities of bodies then 



are 



