1036 TASTE SENSATIONS. [BOOK in. 



On the one hand there is a good deal of evidence to shew a 

 connection between sensations of taste and the chorda tympani 

 nerve. Cases have occurred in which disease of the ear, involv- 

 ing destruction of the chorda tympani within the tympanum, 

 has been followed by loss of taste in the tongue on the same 

 side ; and stimulation of the chorda tympani within the tym- 

 panum has been known to give rise to sensations of taste. 

 Neither of these results is conclusive. The chorda tympani 

 contains afferent fibres which have a remarkable effect on the 

 nutritive processes of the tongue, and the loss of taste due to 

 destruction of the chorda might be due to disordered nutrition 

 of the tongue, and so be analogous to the loss of smell which 

 may follow injury of the fifth nerve. Again, where stimulation 

 of the chorda within the tympanum produces sensations of 

 taste, these may be due to efferent impulses producing changes 

 in the tongue, which in turn give rise to sensations of taste 

 reaching the brain by other channels than the chorda itself ; we 

 have no satisfactory evidence that direct stimulation of the 

 central stump of a divided chorda will give rise to sensations 

 of taste. The connection between the chorda and taste, how- 

 ever, may be of a more real kind. 



On the other hand we must bear in mind how varied and 

 complex are the junctions in the skull between the fifth nerve, 

 the seventh nerve, and the glossopharyngeal nerve, by way of 

 the Vidian nerve, the petrosal nerves, the tympanic plexus, 

 Jacobson's nerve, and the otic and sphenopalatine ganglia. 

 And it seems possible to suppose that fibres leaving the brain 

 by the fifth nerve might find their way not directly to the lin- 

 gual branch but by a roundabout way through the chorda tym- 

 pani, and that at the same time other fibres from the same fifth 

 nerve might ultimately join the glossopharyngeal nerve and 

 reach the back of the tongue by that nerve. There are no cases 

 on record in which disease of the glossopharyngeal nerve within 

 the cranial cavity has led to distinct loss of taste ; but cases 

 have been recorded in which disease of the fifth nerve within 

 the cranial cavity, and so far as could be ascertained limited to 

 the fifth nerve, has led to an entire loss of taste over the whole 

 of one side of the tongue, both back and tip. Such cases lead 

 to the at least provisional conclusion that the gustatory fibres 

 are fibres belonging to the fifth, though they may reach the 

 tongue partly by way of the glossopharyngeal, partly by way of 

 the chorda tympani. 



