288 Dr. Waller's Microscopic Examinatioii of the 



membraneofthepapilla, being also very thin, is easily permeated. 

 On the contrary, the thickness of the epithelial scales over the 

 rest of the surface indicates that there the same action is com- 

 paratively very feeble and slow. It is necessary for a substance 

 to be in a state of solution before it is capable of traversing a 

 membrane, for if merely suspended or floating in a liquid its 

 progress is completely arrested by the membrane. The same 

 remark also applies to the organ of taste, which is only capa- 

 ble of receiving an impression from a body which can be dis- 

 solved in the saliva, or is already in a state of solution. 



To further accelerate the passage tlirough the membrane, 

 the body when placed in contact with the vesicle is subjected 

 to a certain amount of pressure by means of the application of 

 the tongue to the roof of the mouth. The effect of pressure 

 in increasing the action of absorption is well-known from 

 numerous facts ; its influence in the action of taste is shown 

 by the feebleness of the sensation generally caused by a body 

 when merely applied on the surface of the tongue, compared 

 to the acuteness of perception which ensues on its being com- 

 pressed between the tongue and the palate. If the surface of 

 the palate had been entirely smooth, the amount of pressure 

 thus sustained by a substance in a liquid or a pulpy state would 

 be vei'y small, but by the existence of small folds and transverse 

 depressions on its surface the body to be tasted becomes 

 lodged and fixed between them, and thus exposed to a much 

 greater amount of pressure. The importance of this com- 

 pression of sapid substances receives additional evidence from 

 the fact that the gustatory membrane is invariably disposed in 

 a manner to ensure their compression ; and that the soft palate, 

 which likewise has the power of taste, may be regarded as 

 squeezing the sapid substance when passing from the throat into 

 the stomach. 



When the substance is perfectly insoluble, the only sensa- 

 tion of its presence is of a tactile nature, like that of the hand, 

 which enables us to appreciate the size, form, degree of re- 

 sistance and temperature of the body. The resemblance of 

 the papillae conicse to the papillae of the organs of touch, 

 render it very probable that they are destined for the same 

 purposes and fulfill the same functions. The areolar network 

 of the nervous fibres at the base of these papillae is very similar 

 to the terminations of the nerves in the skin, and tends to con- 

 firm the idea of the tactile nature of the papillae conicae. 

 Supposing all impressions to arise from a molecular pertur- 

 bation of the ultimate nervous fibres, the agent in this case, 

 which causes the perturbation, is either simple mechanical 

 contact or caloric. Neither of these agents is liable to accu- 



