CHAP, vii.] OF THE SENSES OF TASTE AND OF SMELL. 411 



as they are applied to the anterior part or the posterior part of 

 the tongue. 1 



The essential structure of the gustatory papillae is still imper- 

 fectly known. Certain anatomists think that the nervous fibres 

 terminate freely in the papillae. Others are of opinion that they 

 anastomose with fine filamentous prolongations emanating from 

 epithelial cells. It is supposed that this arrangement has been 

 observed on the tongue of the frog (Billroth), an animal however 

 in which taste is probably very little developed. 

 . In touch, sensibility is brought into play by the simple shock 

 or contact of bodies. The sense of taste, on the other hand, is 

 only impressionable by solutions, molecules severed in a liquid. 

 But smell demands a matter more attenuated still. In eifect, 

 liquids impregnated with odorous substances awaken no olfactory 

 sensation, at least in man, when they bathe the organ of 

 smell. Substances alone in the state of gases, of vapours, or of 

 line particles suspended in the atmosphere, can provoke olfactory 

 sensations, at least in the superior mammifers. 



In the animal series the anatomical sense of smell is rather 

 better known than that of taste.. Leydig found, in the hirudi- 

 iiates, at the bottom of cupuliform depressions, compact bundles 

 of rigid prolongations, analogous to the tactile baculi. He met 

 with analogous organs in the cephalopodal mollusks. Thinking 

 that he recognised therein olfactory organs, he called these 

 prolongations olfactory baculi. He gave the same name, and 

 attributed the same function to analogous bundles existing on 

 the pair of anterior antennae of certain crustaceans. 2 



In all vertebrates, in which the sense of smell is better and 

 more certainly known, it is also constituted by depressions of 

 varying form and volume situated in the head ; these cavities 

 are usually clothed with vibratile epithelium. In the amphioxus 



1 J. Guyot et Admyrault, Archives Gtnirales de Medcdne, 2 e ser., t. XIII., 

 y. 51. 



2 Gegenbaur, Anatomie Compare, p. 190. Leydig, Histologie Comparee, 

 pp. 250, 361. 



