238 OF SENSATION, AND THE ORGANS OF THE SENSES. 



the tongue and the palate, some sapid substance ; of which the taste is then 

 scarcely recognized, although it is immediately perceived, when its effluvia 

 are drawn into the nose. It is well known, too, that, when the 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 flavour 

 of sapid substances is received through the Smell ; and this is not improbably 

 true : but it is to be remembered, that, besides flavour, 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 cog- 

 nizance. Such sensations are evidently not far removed from those of ordi- 

 nary 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 poi- 

 sonous 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, 



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

 acute; ^education ; and this on the principles already laid down with 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 

 combined 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, more- 

 over, 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 combining 

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

 the unpleasant taste from exciting nausea. 



IV. Sense of Smell. 



324. Of the nature of CEdorous emanations, the Natural Philosopher is so 

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

 account of the mode in which they produce sensory impressions. Although 

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

 solved as it were in the air, and although this idea seems to derive confirma- 

 tion 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 substances that have been impregnating with their effluvia a large 



