604: THE SENSES. 



This effect is easily explained ; since it is well known bow readily move- 

 ment over a free surface, combined with slight friction, will facilitate 

 the solution and imbibition of solid substances. The nervous papillae 

 of the tongue may therefore be regarded as the essential organs of taste, 

 and the lingual muscles as its accessory organs. 



Impressions of taste made upon the tongue remain for a certain time 

 afterward. When a very sweet or a very bitter substance is taken into 

 the mouth, its taste is retained for several seconds after it has been 

 ejected or swallowed. Consequently, if several different savors be pre- 

 sented to the tongue in rapid succession, we become unable to distinguish 

 them, and they produce only a confused impression, made up of the 

 union of various different sensations. The taste of the first, remaining 

 in the mouth, is mingled with that of the second, the taste of both with 

 that of the third, and so on, until neither one can be distinguished. It 

 is notoriously impossible to recognize several different kinds of wine 

 with the eyes closed, if they be repeatedly tasted in quick succession. 



If the substance first tasted have a particularly marked savor, its 

 impression will preponderate over that of the others. This effect is 

 especially produced by substances which excite the general sensibility 

 of the tongue, such as acrid or stimulating powders; and it belongs, 

 in the greatest degree, to substances which are at the same time sapid, 

 pungent, and aromatic, like sweetmeats flavored with the volatile oils. 

 Advantage is sometimes taken of this in the administration of disagree- 

 able medicines. By first taking into the mouth some highly flavored 

 and pungent substance, nauseous drugs may be swallowed immediately 

 afterward with but little perception of their disagreeable qualities. 



Sense of Smell. 



The distinguishing character of the sense of smell is that it gives us 

 intelligence of the physical quality of bodies in a gaseous or vaporous 

 condition. Thus by its aid it is possible to detect the existence of an 

 odoriferous substance at a distance, and although it may be concealed 

 from sight. The minute quantity of volatile material emanating from 

 it, and pervading the atmosphere, produces, by contact with the olfactory 

 membrane, the special sensation of smell. The sense of smell differs, 

 furthermore, from that of taste in being more distinctly localized. While 

 the gustatory sensibility is distributed over the whole mucous mem- 

 brane covering the dorsum and base of the tongue, and is supplied to 

 its various parts by two different sensitive nerves, that of smell is con- 

 fined to the upper portion of the nasal passages and is dependent on 

 the filaments of a single special nerve. 



The mucous membrane covering the superior and middle turbinated 

 bones and the upper part of the septum nasi, which is alone capable of 

 receiving odorous impressions, and is limited by a tolerably well-defined 

 outline, is known as the olfactory membrane. It is easily distinguish- 

 able from that of the rest of the nasal passages: 1st, by its color, which 

 in man, the sheep, and the calf is yellow, but in most of the other mam- 



