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croy has been guided by the chemical nature of substances; but howevef 

 advantageous this last classification may be, it is difficult to include in it, 

 the infinite odours which exhale from substances of all kinds, and it is 

 perhaps as difficult to arrange them in classes, as the bodies from which 

 they are produced. 



This being laid down on the nature of odours, it is next explained, 

 why the atmosphere becomes loaded with the greater quantity, the warm- 

 er and the more moist it is. We know, that in a flower-garden, the air 

 is at no time more loaded with fragrant odours, and the smell is never 

 the source of greater enjoyment, than in the morning, when the dew 

 is evaporating by the rays of the sun. It is likewise, easily understood, 

 why the most pungent smells generally evaporate very readily, as ether, 

 alcohol, the spirituous tinctures, and essential volatile oils. 



CXXV. Oftheorgan of smell. The nasal fossae, within which this organ 

 is situated, are two cavities in the depth of the face, and extending back- 

 ward into other cavities, called frontal, ethmoideal, sphenoidal, palatine, 

 and maxillary sinuses. 



A pretty thick mucous membrane, always moist, and in the tissue of 

 which, the olfactory nerves and a considerable number of other nerves 

 and vessels are distributed, lines the nostrils and extends into the sinuses 

 which communicate with them, and covers their parietes throughout 

 their windings and prominences. This membrane, called pituitary, is 

 soft and fungous, and is the organ which secretes the mucus of the nose; 

 it is thicker over the turbinated bones which lie within the olfactory ca- 

 vities; it grows thinner and firmer, in the different sinuses. 



The smtll appears more delicate in proportion to the nasal fossae being 

 more capacious, the pituitary membrane covers a greater space. The 

 soft and moist condition of this membrane is, likewise, essentially neces- 

 sary to the perfection of this sense. In the dog, and in all animals 

 which have a very exquisite sense of smell, the frontal, ethmoideal, sphe- 

 noidal, palatine, and maxillary sinuses, are prodigiously capacious, and 

 the parietes of the skull are in great measure hollowed by these different 

 parts of the olfactory apparatus; the turbinated bones are, likewise, very 

 prominent in them, and the grooves between them very deep; lastly, the 

 nerves of the first pair are large in proportion. Among the animals 

 possessed of great delicacy of smell, few are more remarkable than the 

 hog. This impure animal, accustomed to live in the most offensive 

 smells, and in the most disgusting filth, has, however, so very nice a 

 smell, that it can detect certain roots, though buried in the earth at a 

 considerable depth. In some countries, this quality is turned to advan- 

 tage, and swine are employed in looking for trufles. The animal is taken 

 to those places where they are suspected to be, turns up the earth in 

 which they are buried, and would feed on them greedily, if the herdsmen, 

 satisfied with this indication, did not drive them away from this substance 

 intended for more delicate palates. 



for example, the lily, the saffron, and jasmine; they fly off readily ; 3d, aromatic, as the 

 smell of the laurel ; 4th, aliaceous, approaching to that of garlic ; 5th, fetid, as that of 

 valerian and fungi ; 6th, virous, as of poppies and opium ; 7th, nauseous, as that of 

 g-ourds, me'ons, cucumbers, and, in general, all cucurbitaceous plants. 



Lorry admits orty- five kinds of odours, camphorated, narcotic, ethereal, volatile acid, 

 and alkaline. 



M. Fourcroy admits the mucous aroma, belonging to plants, improperly termed inodo- 

 rous. Oihj and fugacious, oily and volatile, acid and hydro-sulpfiureous.jlvthor's Note, 



