THE SENSES 849 



ing the latter. They are barrel-like bodies, the staves of the barrel 

 being represented by supporting cells ; each bud encloses a number 

 of gustatory cells with fine processes at their free ends projecting 

 through the superficial end of the barrel. They are surrounded by 

 the end arborizations of the fibres of the gustatory nerves. 



As to the properties in virtue of which sapid substances 

 are enabled to stimulate the gustatory nerve endings, we 

 know that they must be soluble in the liquids of the mouth, 

 and there our knowledge ends. An attempt has been made 

 by various authors to connect the taste of such bodies 

 with their chemical composition, but researches of this kind 

 have not hitherto yielded much fruit. Sapid substances have 

 been divided into four classes : I, sweet ; 2, acid ; 3, bitter ; 

 4, saline. 



Sweet and acid tastes are best appreciated by the tip, and 

 bitter tastes by the base, of the tongue. 



Normal lymph, which bathes the gustatory end-organs, does not 

 excite any sensation of taste, but when the composition of the blood 

 is altered in disease or by the introduction of foreign substances, 

 tastes of various kinds may be perceived. Sometimes this may be 

 due to the stimulation of substances excreted in the saliva ; but in 

 other cases it seems that, without passing beyond the blood and 

 lymph, foreign substances may excite the gustatory nerves. 



When a constant current is passed through the tongue, an acid 

 taste is experienced at the positive, and an alkaline taste at the nega- 

 tive, pole ; and it is said that this is the case even when the current 

 is conducted to and from the tongue by unpolarizable combinations, 

 which prevent the deposition of electrolytic products on the mucous 

 membrane (p. 542). 



Flavour is a mixed sensation, in which smell and taste are both 

 concerned, as is shown by the common observation that a person 

 suffering from a cold in the head, which blunts his sense of smell, 

 loses the proper flavour of his food, and that some nauseous medi- 

 cines do not taste so badly when the nostrils are held. 



In common speech, the two sensations are frequently confounded 

 with each other and with tactile sensations. Thus the ' bouquet ' 

 of wines, which most people imagine to be a sensation of taste, is in 

 reality a sensation of smell ; the astringent * taste ' of tannic acid is 

 not a taste at all, but a tactile sensation ; the ' hot ' taste of mustard 

 is no more a true sensation of taste than the sensation produced by 

 the same substance when applied in the form of a mustard poultice 

 to the skin. 54 



