THE SENSE OF TASTE. 137 



taste of sweetness. Common salt bears a somewhat greater degree of dilution ; 

 the universal remedy for intennittent fever, quinine, remains perceptible under a 

 much greater degree, while sulphuric acid (oil of vitriol) takes rank before all ; 

 water, in which only too^o P''^^'*' ^^ sulphuric acid is dissolved, still tastes 

 perceptibly sour. Acid substances, as many readers both male and female will 

 be able to certify from experiences gained in cookery, most readily impart their 

 sapid qualities. On what conditions these surprising diversities depend, it is 

 beyond our power to explain. 



With one and the same body, the intensity of the sensation of taste v^-hich it 

 excites increases with the progressive concentration of the solution ; a law 

 which needs no other proof than daily experience. As regards the comparison 

 of intensities, it will be well to remember what was elsewhere said on sensations 

 in general, and especially on those of touch ; we have no measure by which we 

 can estimate an impression of taste, so as to give it an exact numerical expres- 

 sion. If we test, one after the other, two solutions of sugar of different concen- 

 tration, we cannot, if the difference is slight, decide which is the sweeter ; we 

 cannot say that one tastes half, twice, thrice, or tenfold as sweet as another 

 with which it is compared. Though this by the way : the intensity of the sen- 

 sation depends not alone on the degree of concentration of the solution, but on 

 several other circumstances, whose agency is in part susceptible of explana- 

 tion, in part not so. It is easily understood that the strength of the sensation 

 increases in proportion as the surface is larger on which the solution operates, 

 and the time longer during which it is in contact with that surface. Just as of 

 two bodies of equal weight that seems to us to be heavier which presses on a 

 larger surface of the skin, and thus gives excitation to a larger number of the 

 nerves of touch, so the same solution of sugar will seem sweeter, if diffused over 

 the whole area endowed with the sense of taste, than when merely a drop of it 

 touches a circumscribed part of the mucous membrane. Thus the intensity of 

 the sensation increases with the sum of the nerve fibres simultaneously excited, 

 because the single impressions seem, in conception at least, to be in some meas- 

 ure combined with one another. The more intense effect produced by prolonged 

 contact of the object with the tongue may be inferred to result from the pene- 

 tration of greater quantities of the substance to the nerve extremities of the 

 mucous membrane; and for this, too, an analogy may be found in the operations 

 of the sense of touch. A hot surface seems less hot on transient than prolonged • 

 contact with the skin, from the circumstance, in the first instance at least, that 

 time is wanting to conduct the particles of caloric in sufficient quantity through 

 the cuticle to the ends of the underlying nerves. One of the most essential 

 conditions for increasing the intensity of a sensation of taste consists in the 

 friction of the solution against the surface of the tongue, or of the latter with 

 the solution against the hard palate. This resource comes into play habitually 

 in the act of taking either solid or liquid food, but we moi-e particularly avail 

 ourselves of it in tasting, with a view to a more accurate judgment of the flavor 

 of any substance. In this case we do not content ourselves with laying the 

 object of which we would form a judgment upon the tongue and quietly await- 

 ing the sensation, but bring it by an incipient movement of deglutition to the 

 hinder part of the tongue, and press this in turn against the hard palate. It is 

 at the moment of this contact, produced by a movement which is indispensable 

 in the act of swallowing, that the most vivid sensation arises, as every one may 

 convince himself who pays attention to what occurs during the process of taking 

 food. For further confirmation of the fact the following experiment may be 

 practiced : Let the tongue be stretched out, with the mouth widely opened, so 

 that the former can no where strike against the roof of the ca*ity, and a drop of 

 dissolved sugar or vinegar be placed upon its surface, only a very weak sensa- 

 tion will ensue, with an instinctive effort to press the tongue against the palate, 

 because we are unaccustomed, except by this means, to conduct the operation 



