854 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



There is strong reason to believe that corresponding to the four primary taste- 

 sensations there are separate centres and nerve-fibres, each of which, when 

 excited, gives rise only to its appropriate taste-sensation. Substances which 

 arouse the sense of taste are not appreciated in uniform degree over the surface 

 of the tongue. Thus, to V. Yintschgau, at the tip of the tongue acids were 

 perceived acutely, sweets somewhat less plainly, and bitter substances hardly 

 at all. It is generally admitted that sweet and sour tastes are recognized 

 chiefly at the front, and bitter, together with alkaline tastes, by the posterior 

 part of the tongue. Strong evidence in favor of the specific difference between 

 various taste-nerves is found in the fact that the same substance may excite a 

 different gustatory sensation according as it is applied to the front or the back 

 of the tongue. Thus, it has been demonstrated that a certain compound of 

 saccharin (para-brom-benzoic sulphinide) appears to most persons to be sweet 

 when applied to the tip of the tongue, but bitter in the region of the circum- 

 vallate papilla?. 1 



Oehrwall 2 has examined the different fungiform papillae scattered over the 

 tongue with reference to their sensitiveness to taste-stimuli. One hundred and 

 twenty-five separate papilla? were tested with succinic acid, quinine, and sugar. 

 Twenty-seven of the papilla? gave no response at all, indicating that they were 

 devoid of taste-fibres. Of the remaining ninety-eight, twelve reacted to suc- 

 cinic acid alone, three to sugar alone, while none were found which were acted 

 upon by quinine alone. The fact that some papilla? responded with only one 

 form of taste-sensation is again evidence in favor of the view that there are 

 separate nerve-fibres and endings for each fundamental sensation; but the 

 figures given in the experiments show that the majority of the papilla? are 

 provided with more than one variety of taste-fibre. 



An extract of the leaves of a tropical plant, Gymnema silvestre, when 

 applied to the tongue, renders it incapable of distinguishing the taste of sweet 

 and bitter substances; it probably paralyzes the nerves of sweet and bitter 

 sensations. When a solution of cocaine in sufficient strength is painted on 

 the tongue, the various sensations from this member are said to be abolished 

 in the following order: (1) General feeling and pain; (2) bitter taste; (3) 

 sweet taste ; (4) salt taste ; (5) acid taste ; (6) tactile perception (Shore). 



That there are laws of contrast in taste-sensation has long been empirically 

 known. Thus, the taste of cheese enhances the flavor of wine, but sweets 

 impair it (Joh. Miiller). It is unfortunate, from a hygienic standpoint at 

 least, that in this most important department of the physiology of sensation 

 investigations are almost wholly wanting. 



Certain tastes may disguise others without physically neutralizing them; 

 when, for example, sugar is mixed with vinegar, the overcoming of the acid 

 taste is probably effected in the central nerve-organ. 3 



1 Howell and Kastle: Studies from the Biological Laboratory of Johns Hopkins University. 

 1887, iv. 13. 



2 Skandinavisches Archivfiir Physiologic, 1890, vol. ii. p. 1. 



3 Brucke : Vorlemngen iiber Physiologie, 1876. 



