212 THE HUMAN BODY. 



that of smell. We must not then confound with natural 

 taste that which smell adds to it, and it is to supply the lack 

 in this respect of what is wanting in our food and in our 

 blunted senses that we make use of condiments. 



We must also distinguish the bodies the action of which 

 is confined to the sense of touch exercised by the tongue, 

 and many impressions reputed to be those of taste ought 

 rather to be considered as purely tactile, such as astringency, 

 tartness, the irritating or caustic action of certain sub- 

 stances, &c. 



On this principle M. Chevreul has divided substances into 

 four classes according to the impression which they produce 

 in the mouth: ist, bodies acting on the sense of touch in the 

 tongue, such as rock-crystal, ice, and so forth; 2d, bodies 

 acting on the sense of touch and of smell, such as aromatic 

 metals, tin and copper for example; 3d, bodies acting upon 

 feeling and taste, as sugar-candy, common salt, &c. ; 4th, 

 bodies acting on the touch, taste, and smell, as mint-lozenges, 

 chocolate, or volatile oils. 



All alimentary substances figure necessarily in the latter 

 class. 



Authors do not agree upon the seat of taste; several be- 

 lieve it extends over nearly the whole surface of the tongue, 

 to the pillars of the fauces, and to the upper surface of the 

 soft palate, to the tonsils, and to the pharynx. It is now 

 generally believed to be located at the tip, at the base, and 

 on the edges of the tongue, and at a certain limited space 

 on the anterior surface of the soft palate. According to M. 

 Longet, the back of the tongue and the pillars of the fauces 

 are not entirely destitute of gustatory sensibility. 



Savoury substances do not produce the same impression 

 upon all parts of the tongue, many salts on the tip of the 

 tongue have an acid, salt, sharp, or styptic, at the base a 

 bitter or metallic taste; others, on the contrary, have the 

 same flavour on every part. In general, acidity is best per- 

 ceived at the tip, and on the edges of the tongue, saline or 

 metallic flavours are developed at the posterior portion. 



In order to perceive the flavour, the savoury molecules 

 must be bathed in saliva, and partially dissolved, so as to be 



