404 ON SENSATION, AND THE ORGANS OF THE SENSES. 



sensibility of the Schneiderian membrane is blunted by inflammation (as in 

 an ordinary cold in the head), the power of distinguishing flavours is very 

 much diminished. In fact, some Physiologists are of opinion that all our 

 knowledge of the flavor of sapid substances is received through the Smell ; 

 and this is not improbably true : but it is to be remembered, that, besides 

 flavor, a sapid body may excite various other sensations, as those of irritation 

 and pungency ; and of these, it seems to be the true function of the sensory 

 surface of the mouth, to take cognizance. Such sensations are evidently not 

 far removed from those of ordinary touch ; and correspond with those which 

 may be excited in the nostrils, through the medium of the Fifth pair. Taken 

 in its ordinary compound acceptation, the sense of Taste has for its object to 

 direct us in the choice of food, and to excite the flow of the mucus and saliva, 

 which are destined to aid in the preparation of the food for Digestion. Among 

 the lower Animals, the instinctive perceptions connected with this sense are 

 much more remarkable than our own ; thus an omnivorous Monkey will 

 seldom touch fruits of a poisonous character, although their taste may be 

 agreeable ; and animals, whose diet is restricted to some one kind of food, 

 will decidedly reject all others. As a general rule, it may be stated, that 

 substances of which the taste is agreeable to us, are useful in our nutrition ; 

 and vice versa: but there are many signal exceptions to this. 



530. Like other senses, that of Taste is capable of being rendered more 

 acute by education ; and this on the principles already laid down in regard to 

 touch. The experienced wine-taster can distinguish differences in age, purity, 

 place of growth, &c., between liquors that to ordinary judgments are alike ; 

 and the epicure can give an exact determination of the spices that are com- 

 bined in a particular sauce, or of the manner in which the animal, on whose 

 flesh he is feeding, was killed. As in the case of other senses, moreover, 

 impressions made upon the sensory surface remain there for a certain period : 

 and this period is for the most part longer than that which is required for 

 the departure of the impressions made upon the eye, the ear, or the organ of 

 smell. Every one knows how long the taste of some powerful substances 

 remains in the mouth ; and even of those which make less decided impres- 

 sions, the sensation remains to such a degree that it is difficult to compare 

 them at short intervals. Hence if a person be blindfolded, and be made to 

 taste substances of distinct, but not widely different flavours (such as various 

 kinds of wine or of spirituous liquors), one after another in rapid succession, 

 he soon loses the power of discriminating between them. In the same man- 

 ner, the difficulty of administering very disagreeable medicines may be some- 

 times got over, by either previously giving a powerful aromatic, or by com- 

 bining the aromatic with the medicine ; its strong impression in both cases 

 preventing the unpleasant taste from exciting nausea. 



4. Sense of Smell. 



531. Of the nature of Odorous emanations, the Natural Philosopher is so 

 completely ignorant, that the Physiologist cannot be expected to give a defi- 

 nite account of the mode, in which they produce sensory impressions. Al- 

 though it may be surmised that they consist of particles of extreme minuteness, 

 dissolved as it were in the air, and although this idea seems to derive confir- 

 mation from the fact that most odorous substances are volatile, and vice versa, 

 yet the most delicate experiments have failed to discover any diminution in 

 weight, in certain substances (as musk) that have been impregnating with their 

 effluvia a large quantity of air for several years ; and there are some volatile 

 fluids, such as water, which are entirely inodorous. The true Olfactory 

 nerves pass down from the Olfactory Ganglion ( 422) in the form of very 



