SENSE OF TASTE. 603 



food, such as tea and coffee, and the various kinds of wine, a great part 

 of the effect produced is due to the aroma or smell which reaches the 

 nares during the act of swallowing. Even in many kinds of solid food, 

 such as freshly cooked meats, their odor takes a very important share in 

 producing the impression on the senses. If, during the deglutition of 

 such substances, the nares be compressed so as to suspend in great 

 measure the sense of smell, their ordinary flavor becomes nearly imper- 

 ceptible ; and a similar effect is produced by catarrhal inflammation of 

 the nasal passages, which suspends more or less completely the sensi- 

 bility of the olfactory membrane. 



Necessary Conditions of the Sense of Taste. There are certain con- 

 ditions requisite for the production of gustatory impressions, beside the 

 integrity of the organ by which they are received. 



In the first place, the sapid substance, in order that its taste may be 

 perceived, must be brought in contact with the mucous membrane in a 

 state of solution. So long as it remains solid, however marked a savor 

 it may possess, it gives no other impression than that of a foreign body 

 in contact with the tongue. But if applied in a liquid form, it spreads 

 over the surface of the mucous membrane, and its taste is perceived. 

 Thus it is only the liquid and soluble portions of the food which are 

 tasted, such as the animal and vegetable juices and the soluble salts. 

 Saline substances which are insoluble, such as calomel or lead carbonate, 

 when applied to the tongue, produce no gustatory sensation. 



The mechanism of the sense of taste is, in all probability, a direct 

 and simple one. The sapid substances in solution penetrate the lingual 

 papillae by endosmosis, and, coming in contact with the terminal nervous 

 filaments, excite their sensibility by uniting with the substance of which 

 they are composed. The rapidity with which endosmosis will take 

 place under certain conditions is sufficient to account for the instanta- 

 neous perception of sapid substances when introduced into the cavity 

 of the mouth. 



It is on this account that a free secretion of the salivary fluids is 

 essential to the full performance of the gustatory function. If the 

 mouth be dry and parched, the food seems to have but little taste. 

 When the saliva, on the other hand, is freely secreted, it mixes readily 

 with the food in mastication, and assists the solution of its sapid ingre- 

 dients; and the fluids of the mouth, impregnated with the savory sub- 

 stances, are absorbed by the mucous membrane, and excite the gusta- 

 tory nerves. 



An important part is also taken in this process by the movements of 

 the tongue. By these movements the food is carried from one part of 

 the mouth to another, pressed against the hard palate, the gums, and 

 the cheeks, its solution assisted, and the penetration of fluids into the 

 papillae more rapidly accomplished. If powdered sugar, or a bitter 

 extract, be simply placed upon the dorsum of the tongue, little or no 

 effect is produced ; but when pressed by the tongue against the roof of 

 the moutli, as in eating or drinking, its taste is immediately perceived. 



