182 PHYSIOLOGY. 



have no communication with tho mouth or gullet. They 



are in .ulaled cavities, covered with a valvular lid, and lined 

 wilh u plaited membrane, similar to tho under surface of 

 oino inushrooniH. This Borvos to extend the surface, while 

 it is covered with a viscid mucus, fin tho cod-fish, the nerves 



of smell are spread mil. iii ii cavity fill'd wilh Hind, and 

 lar',er HI;III Unit which contains the brain itself. "That the. 

 rod is ;niided by Ninrll in the selection of food," says Aitkin, 

 must he well Known to every "lie who has taken it with 



bait, in circumstances whore ho could watch tho conduct of 

 tho finh. If not very hungry, it may frequently bo observed 

 to approach tho bait, apparently attracted by tho Bight, till, 

 at a closer distance, it seems distinctly to smell at it ; and 

 if not satisfied, turns aside and neglects it." Every person 

 who has been in tho habit of fishing much, must have often 

 observed the siiiue tact, in catching common poiid-lish, such 

 as perch, roach, &u. 



11. It was an opinion formerly entertained, that odours 



possess nutritive |ro|>erlies, as savoury smells seem to have 



the effect of allaying hunger, or at least of satisfying tho 

 appetite in some degree. This effect, however, is best ex. 

 plained, by referring it to tho influence of odours on the 



nervous system, Ms we sec the appetite often instantly des- 

 troyed by unwelcome news. In persons whoso digestive 

 organs are weak, tho appetite is often destroyed instantane- 

 ously by a nauseous odour. (We read that Democritus lived 



three days on (he vapour of hot bread ; and I'.acou speaks 

 of a man, who was supported several days by inhaling tho 

 odour of a mixture of aromatic and aliuceous herbs. In 

 IMS, |)r. Wilkins, the Hishop of Chester, published a hook, 

 the object of vtluch was, to :.how that the moon is iiihabil- 

 nble, and that it is possible lor us to find a passage thither. 

 In this work, he says, If we must needs ("eed upon some- 

 thing, why may not smells nourish us ? Plutarch and rimy, 

 and divers oilier ancients tell us of a nation in India, that 



lived only upon pleasing odours; and it is the common 



