378 SPECIAL PHYSIOLOGY. 



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tinguishable from each other, and therefore clearer, and more defina- 

 ble by language, than those of smell. 



Certain properties of substances, which have been named the me- 

 chanical savors, such as the peculiar sensations communicated to the 

 mouth, by oleaginous, amylaceous, or watery substances, are dis- 

 tinguished by the highly developed tactile sensibility of the tongue. 

 They are due to the different degrees of consistency, presented by 

 these bodies. The so-called mealy, sandy, pasty, astringent, and al- 

 kaline impressions, are probably merely special tactile impressions. 

 Pricking, stinging, and biting sensations are perhaps modifications of 

 pain, like the smarting of blistered surfaces. The burning occasioned 

 by some substances, as mustard, and the feeling of cold excited by 

 others, as peppermint, are apparently referable to the sense of temper- 

 ature ; for both these impressions are independent of taste. 



Some substances, when introduced into the mouth, only excite tactile 

 impressions, and hence are called tasteless; all insoluble bodies belong 

 to this class. Other substances, such as sugar, excite both tactile and 

 gustatory impressions; and a third class of bodies, such as smelling- 

 salts and volatile oils, besides producing tactile and gustatory impres- 

 sions, also excite corresponding odoriferous sensations; thus, again, 

 showing the alliance between taste and smell. Lastly, some metals, 

 when placed in contact with the mouth, produce no impression on the 

 gustatory sense, merely exciting tactile and odoriferous sensations. 

 Those substances which act on the gustatory sense, are called sapid. 

 Of these, there are four different kinds, viz., the sour, the saline, the 

 bitter, and the sweet; tartaric acid, common salt, quinine, and sugar, 

 are examples of such substances. Solutions of sour and sweet sub- 

 stances, are said to be best distinguished, when they are applied to the 

 tip of the tongue, whilst saline and bitter tastes are best perceived, 

 when brought in contact with the root of the tongue. Acids and bit- 

 ters are said to be the most readily detected of all sapid substances; 

 then saline, and lastly, saccharine. It has been found, that 1 part of 

 sulphuric acid in 10,000 of water, and 1 part of sulphate of quinine in 

 33,000 of water, can be detected, when carefully compared with pure 

 water. (Valentin.) Sugar cannot be tasted, when there is less than 1 

 part in 80 or 90 of water; and of common salt, 1 part is necessary in 

 200 of water. 



After the tongue has been exposed alternately, in succession, to two 

 or more allied tastes, the gustatory sense becomes blunted, losing its 

 power of discriminating between them. This is probably due, in part, 

 to some continuance of each impression on the gustatory nerves; but, 

 it is perhaps principally dependent on small portions of the sapid bodies 

 remaining dissolved in the epithelial coat. The discriminating powers 

 of the sense of taste, are, on the other hand, assisted by contrasting 

 different flavors. If the tongue be exposed to a temperature much 

 above, or much below, the normal temperature of the body, both its 

 tactile and gustatory sense become impaired or suspended. Thus, 

 after immersion of the tongue in a mixture of broken ice and water, 

 or in water at a temperature of 125, for about a minute the taste of 



