STRUCTURE OF THE TONGUE. 699 



tion of taste that sapid substances in solution should be 

 brought into contact with its nerves. For the nerves of 

 taste, like the nerves of other special senses, may have 

 their peculiar properties excited by various other kinds of 

 irritation, such as electricity and mechanical impressions. 

 Thus Henle observed that a small current of air directed 

 upon the tongue gives rise to a cool saline taste, like that 

 of saltpetre ; and Dr. Baly has shown that a distinct sensa- 

 tion of taste, similar to that caused by electricity, may be 

 produced by a smart tap applied to the papillse of the 

 tongue. Moreover, the mechanical irritation of the fauces 

 and palate produces the sensation of nausea, which is 

 probably only a modification of taste. 



The matters to be tasted must either be in solution or 

 be soluble in the moisture covering the tongue ; hence in- 

 soluble substances are usually tasteless, and produce 

 merely sensations of touch. Moreover, for the perfect 

 action of a sapid, as of an odorous substance, it is necessary 

 that the sentient surface should be moist. Hence, when 

 the tongue and fauces are dry, sapid substances, even in 

 solution, are with difficulty tasted. 



The principal, but not exclusive seat of the sense of 

 taste is the fauces and tongue. 



The tongue is a muscular organ covered by mucous 

 membrane; the latter resembling other mucous mem- 

 branes (p. 403) in essential points of structure, but con- 

 taining certain parts, the papilla, more or less peculiar 

 to itself; peculiar, however, in details of structure and 

 arrangement not in their nature. The tongue is beset 

 with numerous mucous follicles and glands. Its use in 

 relation to mastication and deglutition has already been 

 considered (p. 271). 



Besides other functions, the mucous membrane of the 

 tongue serves as a ground-work for the ramification of 

 the abundant blood-vessels and nerves which the tongue 

 receives, and affords insertion to the extremities of the 



