CHARACTER OF THE SENSE OF TASTE. 377 



the so-called colloid bodies which have a low, diffusive osmotic or 

 dialytic power are tasteless; whilst the crystalloids, which dialyze 

 rapidly, are generally sapid. (Graham.) 



Since many sapid substances, such as quinine and salt, are inodor- 

 ous, the sense of taste must be regarded as independent of smell, as it 

 is of touch, or of the sense of pain. But, in judging of the flavors of 

 different substances, we are assisted by the organ of smell, for many fla- 

 vors are incomplete without the help of the olfactory sense, and may be 

 diminished by closing the fauces, so as to shut off the nose. The exist- 

 ence of nasal polypi also interferes with taste. Certain odors are un- 

 doubtedly confounded with taste. Thus, when eating garlic or vanilla, 

 the sensations referred to the gustatory sense, are no longer perceived 

 when the nose is kept closed. The vapor of chloroform, when inhaled 

 through the nose, conveys the sensation of an odoriferous substance, 

 although it is a sapid body. (Stich.) Deglutition necessarily assists 

 in the appreciation of the taste of sapid substances, when these are 

 grasped by the fauces. 



The sense of taste is, in some respects, allied to the sense of touch. 

 In the first place, it is not dependent on a purely special nerve, for 

 the cranial nerves, through which this sense is exercised, are also 

 common sensory nerves. All the parts concerned in taste, are also 

 endowed with common sensibility. Moreover, for the perception of a 

 gustatory impression, it is essential that the sapid body be brought 

 into actual contact with some portion of the sensory surface, other- 

 wise gustatory impressions cannot be excited. The same is true, how- 

 ever, of the sense of smell, if we regard odors as material. Lastly, 

 as in the case of touch, there is an absence of any complex recipient 

 apparatus, the only structures entering into the formation of the gus- 

 tatory surface, being the mucous membrane of the mouth, with its 

 nervous and vascular papillae, which closely resemble those of the skin, 

 but are more delicate. The sense of taste differs, however, from that 

 of touch, by being limited to a particular portion of the surfaces of the 

 body, and still more remarkably, by the peculiarity of its exciting 

 causes, which are specially chemical and not mechanical agents. In 

 this respect, as already mentioned in the section on Sensation in gen- 

 eral, taste is evidently closely allied to smell. The organ of taste, in- 

 deed, shows greater resemblance to that of touch in structure, than in 

 function. In both, the local application of the exciting stimulant, is 

 necessary; but in the one, the action on the nerve is purely physical, 

 and is merely transmitted mechanically, through the tissues which 

 cover the nerve; whilst in the other, the sapid substance must be fluid, 

 or dissolved, must penetrate the tissues to reach the nerves, and must 

 exercise some very special, and probably chemical action upon them, 

 so as to excite the nervous energy. Bodies differing widely, in both 

 their physical and chemical nature, may excite allied tastes, as for ex- 

 ample, bitter saline substances and vegetable bitters. The causes of 

 the sensation of taste, and of the sapidity or insipidity of different 

 substances, are not further known ; much less can we, at present, offer 

 any explanation of the varieties of tastes excited by different sapid 

 bodies. The sensations induced by them, however, are more dis- 



