CHAP. XV.] CONDITIONS OF TASTE. 445 



of taste, it was found to be clearly absent in the anterior and mid- 

 dle part of the affected side; but to be present behind, in the region 

 supplied by the glosso-pharyngeal. He tasted acutely enough on 

 the other side in front. 



Blumenbach and others relate cases of congenital deficiency of 

 the tongue, in which taste existed. These would show that taste 

 resides in other parts of the mouth besides the tongue, if it were 

 not very probable that a portion of the base of the organ with its 

 gustatory papillae, supplied by the glosso-pharyngeal nerves, existed 

 in these individuals. Without accurate dissections of the parts, 

 such instances throw little light on the question. 



The tongue, as an organ of mastication, is provided with the sense 

 of touch ; the anterior portion, and especially the sides and tip, 

 possessing this sense in an eminent degree. Division of the lingual 

 branches of the fifth nerves in animals is attended with evidence of 

 severe pain, and is immediately followed by loss of sensation in the 

 front part of the organ ; while cases of disease of the fifth nerve in 

 the human subject are marked by loss of sensation in the tongue, 

 in common with the other parts which the nerve supplies. The ex- 

 periments of Alcock and Reid further shew, that mechanical irri- 

 tation of the glosso-pharyngeal nerve in animals is accompanied 

 with manifest pain. Hence there can be no doubt that the lingual 

 branches of the fifth pair are the chief nerves of touch to the tongue, 

 while the glosso-pharyngeal nerves furnish the feeble common sen- 

 sation existing in its hinder part. 



Conditions of Taste.- Taste may be produced by a mechanical or 

 chemical excitation of its nerves. Dr. Baly has observed that a 

 smart tap with the fingers on the tip of the tongue causes a taste 

 sometimes acid, sometimes saline, which lasts several seconds : and 

 galvanism acts in a similar way. Any tasteless substance pressed 

 upon the base of the tongue occasions a bitter sensation, and, if pro- 

 longed, a feeling of nausea. These phenomena shew that the sensa- 

 tion of taste follows excitation of its nerves, however produced : and 

 analogous ones have been observed in connexion with the other sen- 

 sitive nerves. But sapid substances cause taste only when dissolved 

 and made to permeate the tissue of the papillae, so as to come into 

 contact with their nerves. This is proved by the fact that no 

 insoluble substance admits of being tasted, and constitutes a broad 

 distinction between taste and touch; which in some respects approach 

 each other very nearly, particularly in regard to the effects of strong 

 chemical agents on their respective nerves, producing a harsh, pun- 

 gent, burning taste or feel. Taste, like touch, is much influenced by 



