376 SPECIAL PHYSIOLOGY. 



nerve, on the two sides, destroys the power of taste in the parts of the 

 tongue supplied by it. Division of the fifth cranial nerves, or of their 

 gustatory branches, immediately produces loss of common sensibility 

 in the anterior part of the tongue; for the application of caustic pot- 

 ash, or of a hot iron to this part of the organ, in the living animal, 

 does not then give rise to any sign of pain. The power of taste in 

 the forepart of the tongue, has also been said to be destroyed by di- 

 vision of the fifth nerve ; but, as just mentioned, it would seem that 

 except at its edges, and beneath its apex, parts which probably receive 

 filaments from the glosso-pharyngeal, the forepart of the tongue is 

 naturally destitute of the sense of taste. Hence the apparent loss of 

 taste, after division of the fifth nerves, may have been only a loss of 

 common sensibility in the animals experimented on, in consequence of 

 which sapid bodies no longer produced any signs of sensation, either 

 common or special. There is an obvious difficulty in determining very 

 precisely whether an animal tastes or not. In cases of paralysis in 

 man, taste has been destroyed without the common sensibility, and the 

 latter has been lost without the former. This would show, either that 

 different nerves, or different filaments of the same nerves, minister to 

 the two forms of sensation. Whilst it is certain that the glosso-pha- 

 ryngeal is a nerve of taste, the gustatory office of the so-called gusta- 

 tory branch of the fifth nerve is by no means so clearly established. 



It has been observed, that in cases of paralysis of the facial nerve, 

 above the origin of the chorda tympani, in the human subject, the 

 sense of taste is much diminished, or even altogether lost. Experi- 

 ments made by Bernard, on living animals, further show, that if the 

 facial nerve be divided within the skull, the sense of taste is impaired 

 on the corresponding side of the tongue; whilst the tactile sensibility 

 remains unaffected. Division of this nerve, after it has issued from 

 the stylo-mastoid foramen, does not in any way affect the sense of 

 taste. Hence, the integrity of the chorda tympani, which is destitute 

 of sensory fibres, appears to be essential for the proper exercise of 

 taste. Perhaps the effects which follow its division are owing to the 

 diminution which then takes place in the secretion of the saliva. 



A state of solution being an essential condition for the perception 

 of gustatory impressions, sapid bodies are tasteless, when applied in a 

 dry state, to a dry or coated tongue, and a free flow of saliva is of 

 great use in the exercise of the sense of taste. Contact of the sapid 

 body being also essential, it is necessary, for very accurate tasting, 

 that this contact be perfect ; hence, a substance, if solid, must be 

 pressed between the mobile tongue and the palate, so that after it has 

 undergone solution, it may diffuse itself over the whole of the gustatory 

 mucous membrane. In this way, the savors of fruits, and the flavors 

 of wines, become remarkably developed, after these have been carried 

 over the whole of the mucous surface. A short time must elapse, 

 after contact with the tongue, before sapid bodies excite the sense of 

 taste. This varies according to the substance. Saline solutions are 

 most quickly perceived, sweet solutions less quickly, then acid, and 

 lastly, bitter substances. Even when mixed, different substances are 

 tasted separately and consecutively. It is interesting to note, that 



