170 PHYSIOLOGY. 



glands, chiefly during the process of mastication, for the 

 purpose of moistening the food, while the mucous secretion 

 is to keep the tongue in a condition to receive the impression 

 of sapid bodies. For example, in sickness, and especially in 

 fevers, when the mouth is dry and parched, owing to a sup- 

 pression of this secretion, the taste is entirely lost, showing 

 that the membrane of the tongue must be kept moist in order 

 to the preservation of the taste. 



6. Insoluble substances are totally insipid, because in order 

 to affect the nerves, the substance musH>e in such a state as 

 to penetrate the spongy papillae, (it is supposed that the 

 salts which enter into the composition of the saliva, are very 

 efficient agents in reducing substances to a proper condition 

 for making an impression on the gustatory organ^ In this 

 way, we can account for the fact, that metals, though in- 

 soluble in water, often impart a peculiar taste. The organs 

 of taste are also powerfully affected by metals, so applied tc 

 the mouth as to call forth electric action. If we place ont 

 kind of metal on the tongue and another under it, and then 

 bring their edges together, a strong sensation is experienced 

 If we touch the surface of the tongue with the point of a 

 wire, connected with the positive pole of a galvanic battery, 

 a sour taste is experienced ; while the negative pole excites 

 an alkaline taste. fThese phenomena may be owing either 

 to the electric action, disengaging from the saliva an acid 

 in one instance, or an alkali in the other, or the electric ex- 

 citement may call forth the special sensibility of the gusta- 

 tory organ, in the same manner as it causes the special 

 sensibility of the other organs. ) 



7. Savours, like odours, are innumerable, and as they dif- 

 fer so much from each other, it is impossible to classify them 

 in any satisfactory manner. We can readily understand 

 what is meant by the terms sweet, Utter, sour, saline, acr'uly 

 &c., yet each of them differs in intensity, as well as other 

 shades of character. For example, rectified sugar, brown 

 sugar, maple sugar, beet sugar, molasses, honey, &c., are all 



