OF NATURAL HISTORY. i6i 



Our obfervations on the different inftruments of fenfatlon fliall 

 proceed in the following order, namely, of the fenfes of fmelling, 

 of tafting, of hearing, of touch, and of feeing. In general, it may 

 be remarked, that all fenfation is conveyed to the mind by an un- 

 known influence of the nerves. If the optic, olfadtory, or any 

 nerve diftributed over an organ of fenfation, be cut, or rendered pa- 

 ralytic, the animal inftantly lofes that particular fenfe. This is a 

 fad univerfally eflablifhed by experiment. But that the nerves, 

 which are perfedly fimilar in every part of the body, fhould, when 

 diftributed over the eye, the ear, the tongue, the nofe, convey to the 

 mind feelings fo different, is the moft myfterious part of this fubjedt. 

 When M. de Bonnet tells us, that every organ of fenfe probably 

 confifts of fibres fpecifically different ; and that thefe fibres are par- 

 ticular fenfes endowed with a peculiar manner of adting, correfpond- 

 ing to the perceptions they excite in the mind ; — he means to reafon; 

 but he does no more than give a circumlocution for the fad:. 



OF SMELLING. 



IN man, and many other animals, the organ by which the fenfe 

 of fmelling is conveyed to the mind, has received the general appel- 

 lation of nqfcy or noflrih. The more immediate inftrument of this 

 fenfation is a foft, vafcular, porous membrane, covered with nume- 

 rous papillae, and is known by the name of membrana pitiiitaria, or 

 membrana Schneiderlana. This membrane is totally covered with 

 infinite ramifications and convolutions of the olfadory nerves. Thefe 

 nerves are almoft naked, and expofed to the adion of the air which 

 pafles through the nofe in performing the fundion of refpiration. 

 But Nature, ever attentive to the eafe and convenience of her crea- 

 tures, has furnifhed the noflrils with a number of glands, or fmall 

 arteries, which fecrete a thick infipid mucus. By this mucus, the 

 2 t X olfadory 



