738 OF THE ORGANS OF THE SENSES, AND THEIR FUNCTIONS. 



which one or more fasciculi are given off, that run up the axis of the papilla, 

 and then break up into numerous fine branches which stream out towards 

 the epithelium. In the Frog, cylindrical papillae are present, which are 

 composed below of loose, and near their free extremity of compact, connec- 

 tive tissue, forming a nerve-cushion ; upon each of these lies a gustatory disk, 

 the structure of which is analogous to that of the gustatory bulb, being re- 

 solvable into goblet and columnar supporting or protecting cells, and forked 

 cells, which appear to be the continuation of the uon-medullated nerve-fibres 

 (Fig. 256). 



602. The simple application of a sapid substance to the gustative surface 

 is usually sufficient to excite the sensation ; and if this application be re- 

 stricted to one particular spot, we are able to recognize its place more or less 

 distinctly. In this respect, then, the gustative impression resembles the 

 tactile ; for whilst we cannot by our own consciousness, distinguish the parts 

 of the retina or of the auditory apparatus on which visual or auditory im- 

 pressions are made, we can make this distinction in regard to the surface 

 which is supplied by the nerves of general sense. From the careful ex- 

 periments of Stich and Klaatsch, 1 supported as they are by the results of 

 other observations, we are now enabled to define with some accuracy the 

 exact seat of the sense of taste. It exists over the whole surface of the 

 posterior third of the dorsum of the tongue, on the under surface of the tip, 

 and in a band or line, about one-quarter of an inch broad, running along 

 its edge. The sense is also well defined in the posterior part of the hard 

 palate, and in that portion of the soft palate which is near the bone, and 

 lastly, in the anterior pillars of the fauces. The middle and anterior part 

 of the dorsum, the gums, posterior pillars of the fauces, and the inner sur- 

 face of the lips, possess no sense of taste, though exquisitely sensitive to 

 tactile impressions. Bitters and acids appear to be the substances of which 

 the dilution or attenuation may be carried to the greater extent, without 

 ceasing to excite sensations of taste, providing a sufficient volume of the 

 solution be introduced into the mouth. Thus, according to Valentin, one 

 part of extract of aloes or of sulphuric acid in 900,000 of water, and even 

 one part of sulphate of quinine in 1,000,000 of water, may be distinguished 

 if heedfully compared Avith perfectly pure water. The contact of a sapid 

 substance much more readily excites a gustative sensation, when it is made 

 to press upon the papillae, or is moved over them. Thus there are some sub- 

 stances whose taste is not perceived when they are simply applied to the 

 central part of the dorsum of the tongue, but of whose presence we are at 

 once rendered cognizant by pressing the tongue against the roof of the 

 mouth. The full flavor of a sapid substance, again, is more readily per- 

 ceived when it is rubbed on any part of the tongue, than when it is simply 

 brought in contact with it, or pressed against it. Even when liquids are re- 

 ceived into the mouth, their taste is most completely discriminated by caus- 

 ing them to move over the gustative surface: thus the "wine-taster" takes 

 a small quantity of the liquor into his mouth, carries it rapidly over every 

 part of its lining membrane, and then ejects it. It is not improbable that 

 this exultation of the usual effects is simply due to mechanical causes; the 

 sapid particles being brought by the pressure or movement into more rapid 

 and complete operation on the nerve-fibres, than they would be if simply 

 placed in contact with the papilhe. The rapidity with which sapid impres- 

 sions are perceived has been made the subject of a series of experiments by 

 Vintecbgau and Honigschmied. 2 The substances used were bisulphate of 



ArHiiv f. Path. Anat., Bd. xiv, 1858, p. 225, and Bd. xviii, p. 80. 

 2 I'lluger's Archiv, 1875, pp. 1-48. 



