SENSE OF TASTE. 697 



of air into the tympanum, so as to make tense the mem- 

 brana tympani; and in the act of blowing the nose, as 

 well as during the forcible depression of the lower jaw. 



Irritation or excitement of the auditory nerve is capable 

 of giving rise to movements in the body, and to sensations 

 in other organs of sense. In both cases it is probable 

 that the laws of reflex action, through the medium of the 

 brain, come into play. An intense and sudden noise 

 excites, in every person, closure of the eyelids, and, in ner- 

 vous individuals, a start of the whole body or an unpleasant 

 sensation, like that produced by an electric shock, through- 

 out the bodj r , and, sometimes a particular feeling in the 

 external ear. Various sounds cause in many people a 

 disagreeable feeling in the teeth, or a sensation of cold 

 tickling through the body, and, in some people, intense 

 sounds are said to make the saliva collect. 



The sense of hearing may in its turn be affected by im- 

 pressions on many other parts of the body ; especially in 

 diseases of the abdominal viscera, and in febrile affections. 

 Here, also, it is probable that the central organs of the ner- 

 vous system are the media through which the impression 

 is transmitted. 



SENSE OF TASTE. 



The conditions for the perception of taste are : I, the 

 presence of a nerve with special endowments ; 2, the 

 excitation of the nerves by the sapid matters, which for 

 this purpose must be in a state of solution. The nerves 

 concerned in the production of the sense of taste have been 

 already considered (pp. 547 and 555). 



The mode of action of the substances which excite taste 

 probably consists in the production of a change in the 

 internal condition of the gustatory nerves ; and, according 

 to the difference of the substances, an infinite variety of 

 changes of condition, and consequently of tastes, may be 

 induced. It is not, however, necessary for the manifesta- 



