Abstract
EDINBURGH Royal Society, July 19.—The sense of taste, by John B. Haycraft. Sensation or feeling is a result of the operations of the external world upon our sentient bodies. A vibration of light, a sonorous wave, a molecule of sugar or of musk stimulates the appropriate nerve through the mediation of a little sensitive cellule in the eye, the ear, the tongue, or the nose. A motion called a nerve motion is then set up, passes to the brain, and if this organ is in a state of activity we are conscious of a feeling or sensation. In the case of sound and light the character of the vibration determines the quality of the sensation produced. Thus, a certain complex vibration of light produces a sensation we call crimson, a certain complex vibration of sound we recognise as coming from a violin-string. Motion is thus transmitted into a nerve motion or impulse, which gives rise to a sensation. Of the thousand qualities of sensation all have a counterpart in the thousand variations of motion outside the body. The physiologist knows little more about the production of the sense of taste than those facts which are the intellectual property of every one. The object of the author of the paper of which this is a short abstract is to show that taste in its method of production is precisely analogous to sight and hearing. The truth of this is indicated by the striking similarity in structure between the end-organs of all the special senses, which are all developed from primitive ectodermic cells, of much simpler form. Spectroscopic investigation has demonstrated, too, that the sapid and odorous molecules vibrate constantly and in a manner characteristic of each substance. We have, then, in the case of taste (and it is hoped subsequently to demonstrate this in the case of smell as well), vibrating matter and a sensitive end-organ, conditions analogous with those present in the other senses. If it can be shown that substances vibrating in the same manner produce the same taste, the analogy will be complete. It has been found by Newlands and others that if the elements be arranged in a series, starting with that metal which has the lowest, and passing up to that which has the highest, atomic weight, a periodic recurrence of chemical and physical properties is observed. Thus lithium, the second in the series, is similar to sodium, the ninth, and potassium, the sixteenth, and so on. This is called the periodic law. The author finds that there is also a periodicity as regards taste production. Thus the chlorides or sulphates of a series of similar elements—called a group of elements by Mendelejeff—have similar tastes. It is curious, however, that the taste changes slightly but uniformly as we pass to the higher members of a group. Thus the chlorides of lithium and sodium are salt, but as you pass to the higher members of the group the taste becomes more saline and very slightly bitter. Now Prof. Carnelley has recently discovered that compounds containing elements of the same group have similar colours, the colour changing, however, uniformly—passing to the red end of the spectrum—as we reach the higher members of a group. Colour is periodic. But this indicates that the elements of the same group are vibrating in a similar way. If the lower member be yellow from absorption of the blue, the next one will have vibrations of nearly the fame pitch, being in reality at a somewhat slower rate of vibration, and absorbing rays nearer the red end. Here, then, is the analogy sought for. A group of salts of similar chemical properties have their molecules in a similar vibrating condition, giving rise to similar colours and similar tastes. A study of the carbon compounds yields as conclusive evidence. The alcohol bodies, such as mannite, grape-sugar, glycerine, glycol, are sweet. They possess a certain common molecular structure and a compound radical, CH2.OH. Associated with this radical is the taste called sweet, just as are associated with it many chemical and physical properties. Common alcohol is tasteless, but it is monatomic, all the polyatomic alcohols having a sweet taste. The organic acids, too, have a radical, CO.OH, with which seems to be associated their acid properties and the power of producing a special taste. Now it is certain that compound radicals, like elementary substances, vibrate in a definite way, however they are combined. A coloured acid like chromic and picric acid forms a class of coloured salts. Ammonia viewed in quantity shows characteristic absorption-bands; replace an atom of hydrogen by ethyl or methyl, and the same bands are to be observed, shifted, however, slightly towards the red end of the spectrum. We see, then, in the carbon compound the radical vibrates, modifies light passing through it in a definite way, and affects the sensorium by causing the production of a definite sensation of colour. So too it can produce a definite taste sensation. I do not hazard an opinion as to how the molecule stimulates the end-organs in the tongue. Too little is known about the stimulation of the retina by light. Whether or not in both cases it is mechanical, one cannot say. As to its being chemical action, it may well be asked, What is this? Chemical action itself may perhaps be most satisfactorily interpreted by the use of a mechanical hypothesis. Much has yet to be discovered as to the exact relationship between vibration and taste sensation. That this relationship exists, is all the author wishes to prove. When spectroscopic investigation of the invisible spectrum is more advanced, what Helmholtz has done for sound may also be done for taste, and we may know the exact vibrational counterpart of a taste quality as we know it already of the sound of a violin-string.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 34, 515–516 (1886). https://doi.org/10.1038/034515a0
Issue Date:
DOI: https://doi.org/10.1038/034515a0