All sapid bodies are soluble, but the physical qualities of insoluble bodies can be also ascertained by the tongue, which we mentioned has exquisite tactile sensibility. The Filiform, Fungiform, and Calyciform Papilla. All sapid substances belong to the class of bodies which Graham terms "crystalloid," for the "colloid" substances are not able to diffuse through the membrane which coats the surface of the papillæ. The palate, cheeks, and upper part of the pharynx have slight gustatory power-so that in Blumenbach's case of congenital absence of the tongue, the sense of taste was still present. The exquisite sensibility of the sense of taste may be judged by the minute quantities of various sapid substances which it can distinguish; thus, I have found that Too of a grain of strychnia in a drachm of water gives a distinct bitter taste. Taste is much aided by smell, and the two functions are usually exercised together; either pleasant or nauseous flavours are much decreased by holding the nose so as to prevent the odour of the body which is being tasted from passing through the nares. Pressure and prolonged application of the sapid body favour taste, and some substances leave a most persistent impression on the organ. A certain taste is occasionally followed by the subjective sensation of an utterly different one; thus, many sweets give rise to a bitter after-taste, and tannin, which is intensely bitter at first, tastes somewhat sweet after a while. It depends on exhaustion of the nerve to one stimulus, and is analogous to the phenomena of complementary colours. After frequent use, the papillæ seem to lose their gustatory power, for if the tongue be protruded and salt and sugar applied alternately, we cannot after a while distinguish between them until the tongue is applied to the palate. If the tongue be kept in water either at 125° or 32° for a minute, it loses all gustatory or tactile endowments. The relative gustatory power of various parts of the tongue may be ascertained by applying sapid bodies in capillary tubes, or by covering it with a glove of softened parchment, with apertures where we wish to make the experiment. Electric currents, a smart tap, or a stream of air, produce gustatory impressions on the tongue. As an instance of subjective sensation of taste, Magendie states that dogs licked their lips and seemed to taste when he injected milk into their veins; but some of that fluid may have been conveyed to the lingual papillæ, and have thus produced a real objective effect. In the same way the bitter taste often existing in the mouth during indigestion may be due to biliary matter being brought to the organ of taste. The trifacial, glosso-pharyngeal, and lingual nerves may be here conveniently considered, as these cranial nerves endow the tongue with its peculiar functions. The Trifacial, usually numbered the 5th nerve, is remarkably analogous, as Sir C. Bell noticed, to the spinal nerves in having a sensitive and ganglionic root, which a motor twig then joins. The inferior maxillary branch is compound, in the sense of having a motor and sensitive portion, but it gives off separate motor and sensitive twigs, and none of which are really mixed in function. The nerve seems to arise from the side of the pons, but Prof. Alcock, late of Queen's College, Cork, traced it to the groove on the floor of the 4th ventricle. The sensitive root forms the Casserian ganglion, and then divides into 3 portions, the distribution of which is as follows: I. OPHTHALMIC 1. Frontal 2. Lacrymal 3. Nasal Supra-trochleator, to skin of eyelids, Supra-orbital, to skin of forehead. To conjunctiva. To join the facial nerve through malar A root to the lenticular ganglion. The infra-trochleator, to inner canthus The proper nasal II. SUPERIOR MAXILLARY 1. Temporo-malar, joining lacrymal, supplies malar and temporal regions. 2. Spheno-palatine, to Meckel's ganglion. 3. Posterior superior dental. 4. Infra-orbital, to the skin of the face. III. INFERIOR MAXILLARY 1. Inferior dental, which sends the mental branch to the skin of the face. 2. Gustatory, to lingual papillæ. 3. Temporo-auricular, to the skin of ear and temple. The branches from the motor division are: 4 & 5. Temporal 6. Masseteric. 7. Buccal. 8. Pterygoid. 9 & 10. Mylohyoid and digastric, which accompany the inferior dental. The functions of this great nerve may be ascertained in 3 ways-1. Its distribution. All these nerves are sent to sensitive surfaces, except the last six, which supply and associate the muscles of mastication. Two of these muscles, the buccinator and digastric, also are concerned in respiration, and thus receive a second supply from the facial nerve. 2. By experiment. Irritation of the motor root causes spasm and division of it, paralysis of all the masticating muscles. Very remarkable effects follow the section of the sensitive root. One side of the face is rendered quite insensible, and irritants may be applied to the conjunctiva, nasal surface, or mouth without any effect. The conjunctiva becomes dry, the cornea grows dull, then quite opaque, and at last sloughs, and the entire eye is destroyed. These effects are partly due to the lodgment of dust which excites destructive inflammation, and in a greater degree to the impairment of nutrition. Many believe that it is the injury to the sympathetic, necessarily occurring in such experiments, which gives rise to these morbid changes. Division of the supraorbital branch often produces amaurosis, a fact which cannot be satisfactorily explained. 3. Disease, such as softening of the portion of the brain where it arises, or tumours pressing on the nerve, produce complete anæsthesia of the whole side of the face, and in some cases the motor branch and the masticatory muscles are involved. If an object be pressed on the lips, the contact on the diseased side will not be perceived, and the patient often observes that there is a bit broken off the vessel he drinks from. The supra-orbital, infra-orbital, and mental twigs are the nerves affected in tic douloureux or facial neuralgia. This painful affection is often temporarily excited by some irritant, such as an ice in the stomach; and on the other hand the fifth nerve is very often the excitor nerve in many convulsive diseases which dentition gives rise to. It is also the exciter to the function of respiration, and thus in cases of fainting we often induce an inspiration by dashing cold water on the face. The Glosso-Pharyngeal arises in a grey mass within the olivary body, and passing between that body and the restiform, emerges through the jugular foramen, where it forms the ganglion of Ehrenrittér, and below this a larger one, that of Andersch. The nerve then runs with the stylo-pharyngeus muscle, and breaks into branches, for the muscles and mucous membrane of pharynx, and for the lingual papillæ. Those branches. which go to the pharynx are purely sensitive, but either by mixing with some filaments from the spinal accessory or pneumogastric, or by referring an impression to the medulla, irritation of them produces motion of the pharynx. The glosso-pharyngeal is then the centripetal nerve of deglutition. We shall now discuss the question whether the gustatory or glosso-pharyngeal is the nerve of taste. Valentin asserted that the latter alone was the nerve of taste, as he found that sense was lost on its section. Panizza found that after section of these nerves dogs eat food mixed with colocynth, for which substance they have an extraordinary aversion. And again, the swan and parrot possess taste, although no branch of the fifth supplies their tongue. Experiments have, however, set the question at rest, for it has been proved that the gustatory nerve presides over taste in the anterior part of the organ, where the sense is more acute; and the glosso-pharyngeal at the back, which supplies the calyciform papillæ, where impressions are more enduring. The Lingual nerve arises between the pyramid and olivary body, escapes through the anterior condyloid foramen, communicates with the cervical plexus and gustatory nerve, and supplies all the extrinsic muscles of the tongue. The lingualis or intrinsic muscle is supplied by the facial nerve, through the corda tympani, |