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



either entirely inodorous, or so nearly as only to be recognizable through its 

 means when in large masses ; and the most refined touch cannot afford any 

 indication of that kind of difference among them, of which we are at once 

 rendered cognizant by taste. Of all the "special" senses, however, that of 

 Taste is most nearly allied to that of touch, as appears from several con- 

 siderations. In the first place, the actual contact of the object of sense Avith 

 the organ through which the impression is received, is necessary in the pres- 

 ent case, as in the preceding. Again, it appears from the considerations 

 formerly adduced ( 493), that there is no special nerve of Taste; for the 

 gustative impressions upon the front of the tongue are conveyed by the 

 Lingual branch of the Fifth pair, and the branches of the Facial running 

 in the Chorda tympani, 1 whilst those made upon the back of the organ are 

 conveyed by the Glosso-pharyngeal, both of which nerves also minister to 

 common sensibility ; and pressure on the trunk of either of these nerves 

 gives rise to pain, which is not the case with either the olfactory, the optic, 

 or the auditory nerves. Moreover, the papillary apparatus, through which 

 the gustative impressions are made upon the extremities of these nerves, 

 is essentially the same in structure with that of the skin. 2 



600. For the Gustative nerve-fibres to be impressed by the distinctive 

 properties of sapid substances, it appears requisite that these substances 

 should be brought into immediate relation with them, and that they should 

 penetrate, in the state of solution, through the investments of the papilla?, 

 into their substance. This would seem to be proved by the two following 

 facts: first, that every substance, whether solid, fluid, or gaseous, which 

 possesses a distinct taste, is more or less soluble in the fluids of the mouth, 

 whilst substances which are perfectly insoluble do not make their presence 

 known in any other way than through the sense of touch ; and, second, that 

 if the most sapid substance be applied in a dry state to the papillary sur- 

 face, and this be also dry, no sensation of taste is excited. Hence it may 

 be inferred that in the reception of gustative impressions, a change is pro- 

 duced in the molecular condition of the nerve-fibres, or, to use the language 

 of Messrs. Todd and Bowman, their polarity is excited by the direct agency 

 of the sapid matter itself. This change may be induced, however, both by 

 electrical and by mechanical stimulation. If we make the tongue form part 

 of a galvanic circuit, a peculiar sensation is excited, which is certainly allied 

 rather to the gustative than to the tactile, and which does not seem to be 

 due (as was at one time supposed) to the decomposition of the salts of the 

 saliva. And, as Dr. Baly has pointed out, 3 " if the end of the finger be 

 made to strike quickly, but lightly, the surface of the tongue at its tip, or 



1 Lussana, Centralblatt f. d. Med. Wiss., 1871, p. 233. 



2 For some pathological cases bearing upon the question of the implication of the 

 chorda tympani in the sense of taste, see Inzani and Lussanna, in the Annali Uni- 

 versal! di Med., 1802, pp. 282-322; Stich, in Henle and Meissner's Bericht, IS.'.?, 

 p. 588; whilst for experimental evidence to the same effect, see Schiff, Untersueli. xur 

 Naturlehre, Bd. x,p. 406, and E. Neumann. Konig<herger Medic. Jahrb., Bd. iv, p. 1. 

 The two former observers believe the chorda tympani to be the true nerve of taste 

 for the anterior part of the tongue, by which sweet, saline, piquant, and aromatic 

 flavors are distinguished, whilst the mineral acids, astringents, bitters, pungents 

 putrefactive, and disgusting flavors are chiefly perceived through the glosso-pliarvn- 

 geal. Seh iff, Physiologic, 1859, p. 403, thinks the Glosso-pharyngeal nerves 'are 

 especially adapted to perceive bitter, and the Fifth nerves acid tastes. Moos, Cen- 

 tralblatt, 1SU7, No. 46, records a case where modifications of the sense of taste in the 

 forepart of the tongue resulted from pressure on the chorda tympani, occasioned by 

 the use of one of Toynbec's artificial tympana. 



3 Translation of Mailer's Physiologic, p. 1062, note. 



