English
The nerve track has not PHYSIOLOGY 8S yet been definitely known, btit it is supposed to terminate in the hippocampal convolution,, posterior to the olfactory lobe. The gustatory sensation is possibly complex. There are but four fundamental taste sensations, —namely, sweet, bitter, acid, and salty and the rest are but the combinations of these primary tastes, for’ the experience of which we are dependent on the terminal organs which are chiefly present in the fungiform and circumvalhite papillae. And there are so many complex and multiple junctions between the fifth nerve, the seventh nerve and the glossopharyngyal nerve, by way of the Vidian nerve, petrosal nerves, tymphanic plexus, the otic and the splenopalatine ganglia, that it is hard to determine, how the taste sensation travels, but perhaps through the chorda tympani nerve. In the nasal sepUim and a portion of the tipper turbinate bone, the area coi’responding to about 250 square millimeters in each nostril, there is a profuse distribution of the fibres of the olfactory {gandha) nerve, in the shape of elongated, epithelial like cells, each of which bears on its end a tuft of six to eight hair-like processes. And there are tiny glands which keep the mucous always humid and moist. 83 AKCIENT HINDU MEDICINE Particles of odoriferous matters, carried in a gaseous medium, namely the air, to the olfactory epithelium, become dissolved in the thin layer of fluid that keeps the nasal membrance moist¬ ened and this percolates through and stimulat¬ es the nerve-endings. But if the membrane be too dry or the secretion be too abundant or altei’ed in quality, the power of smelling is diminished and even may be wholly suspended. The olfactory nerve terminates in the cox'tex of the brain in the ‘cornu Ammonis and hippo¬ campus' The animals with highly developed sense of smell possess a large ‘limbic lobe.' Some of the substances retain their odoriferous quality even in minute dilution as camphor 1; 400,000 ; musk 1 : 8,000,000 ; vanilin' 1 : 10,000,000 parts. The touch {sparsa) is a compound sensation of pressure, warmth, cold and pain, through lour distinct kinds of nerve-fibres which are not only richly distributed over the general cutaneous surface, but also in the buccal and rectal membranes. But the alimentary mem¬ branes, or the superfacise in the interior of the body are supplied with nerve-fibres of pain and devoid of those of touch and temperature sensations. Application of cocaine on the eye PHYSIOLOGY SS’ or throat paralyzes the feeling of pain and pressure, but the sensations of heat and cold are not influenced, • which proves that their nerve- fibres are different and mediate through different channels. It has been clinically observed that the compression of the cords of the brachial plexus, resulted in the insensiblity of the arm to pressure and temperature, but not of pain. And it is supposed the nerve-endings of pain lie deeper than the tactile senses, which are superficial; the former mediating through the spinal cord and the latter through the posterior funiculi, together with some of the fibres of the muscle sense and they do not cross until after tliey reach the medulla and perhaps they are represented in the rolandic area. The vocal sound or voice {ghosa) is distinct from speech, which is an articulate sound to express definite ideas. The animals are endotr- ed with vocal power, but not with speech. And there may be speech without voice as in whisper¬ ing and voice without speech as in singing a musical tone. The vocal organ, the larynx, resembles to a great extent the siren in the production of tone. The larynx is a framework of cartilages, connected with elastic ligaments, which are vocal cords, and it opens above into 86 ANCIENT HINDU MEDICINE the cavity of the pharynx and below into the trachea or windpipe. With respiration, the lung acts as bellows, pressing h. blast of air through the thin tube of the windpipe and the escaped air is modulated by the movable liga¬ ments into various tones. The voice has three eharacteristics, (1) ‘loudness* which depends on the force of the expiratoi’y blast; (2) ‘pitch* which depends on the rapidity of vibrations and (3) the ‘quality* which depends on the capacity of the resonance chamber and the muscular strength and pliability of the laryngeal liga¬ ments (vocal cords). The alternate expansion and contraction of the ligaments and muscles of the larynx (glottis) are made by the bulbar and recurrent laryngeal nerves. If any of these nerves is destroyed, the rythmic widening and narrowing automatically cease and the glottis remains immobile and no voice (vocal sound) can be produced. There are four speech (bhasa) centers^ situat¬ ed along the Sylvian fissure, in the left hemi¬ sphere for the right-handed and in the right hemisphere for left-handed individ^uals. The motor center for pronouncing and articulating words, occupies the foot of the third frontal convolution (left), immediately in front of the PHYSIOLOGY 87 s centers of phonation, vitilized in speech. The desti’uction of this center produces motor aphasia {apheniia). In aphemia one is able to hear and to understand when spoken to, and is able to emit sound, to move the tongue and the lips, hut he has lost his vocabulary, in other words, the faculty to articulate words. But if the injury is not complete, that is, in partial aphemia, the patient can utter a few incoherent words and syllables according to the nature of the lesion. The center for auditory images, that is, for comprehending spoken w^ords, occupies the posterior fourth of the first tempo¬ ral convolution (left). The destruction of this center causes sensory aphasia (word-deafness). In sensory aphasia, one can hear the A^oice, as the faculty of hearing is not affected, hut he can not understand the spoken words, and the words are to him mere sounds and do not express any idea. The center for visual graphic images, that is, for distinguishing written or printed words, occupies the left angular gyrus(posterior inferior ,part of the left parietal lobe). The destruction of this center causes alexia (word- hlindness). In alexia, one can not read even his own writing, although his vision and intelli¬ gence are not affected and he can see the form 88 AXCIENX HINDU MEDICIEN of the letters, but has lost the faculty of comprehending ideas, expressed through those words. The center for the faculty of writing, is situated at the foot of the second frontal convolution and the destruction of this center- produces the inability to write {agraphia). In agraphia, one has lost his faculty of expressing his ideas in writing or any graphic form. Agraphia is usually associated in clinical experience with motor aphasia {aphemia). Sleep {nidra) is evidenced by the cessation of sensory-motor reaction. Various hypotheses have been advanced to explain' the causation' of sleep. (1) Cerebral anemia was suggested by the old Avriters ; but it is rather the effect than- the cause of it. (2) Hyposecretion of the thyroid due to the inhibitive action of the accumulative waste products during waking hours and the hyper-secretion of the pituitary body; but in myxedema, drowsiness is not constant, nor is there any proof that in hypnotic or epileptic somnolence, there is any increased secretion of hypophysis, or diminished secretion of the thyroids. (3) Osmotic theory of Devaux, Avhich tries to explain sleep due to the increased viscoeity of blood, through dehydration, is not bsustantlated by observation, as in privation of PHYSIOLOGY 89 water—in thirst, the nervous system is rather ii’ritatecl. (4) Chemico-toxic theory enjoys a better reputation. The accumulated tissue* waste products as lactic acid, cholesterine, leucomaine, exercise an inhibitory action on the cerebral activity, either paralyzing the centre directly, through intoxication or indirectly by reflex vaso-constriction. (5) Accumulation o£ carbonic acid which has an extreme avidity for oxygen, reduces the minimum ratio of free oxygen, necessary for the central nervous activi¬ ties. (6) Consumption of the intramolecular oxygen causes cerebral asphyxia, which is expressed as sleep, as during the waking hours,, the brain cells use up their store of oxygen more rapidly than it can he replenished by absorption from blood ; the consequence is that for lack of respiration, the brain-cells can not react to the sensory stimuli and gradually losing conscious¬ ness, store up sufficient oxygen through the anabolic process to be awakened up again. (7) The neuron theory tries to explain sleep on the histological principle that the nerve track is not continuous like the electric wire, but composed of the cell-units (neuron) which, transmit their impulse from one to the other by their contact through the interlacings of dendrid- 90 ANCIENT HINDU MEDICINE ed and terminal arborizations, and when there is sufficient accumulation of fatigue products, the dendrides contract and retract, so that the nerve-path being broken and the brain being automatically relieved from sensory stimulation, sleep is mechanically produced. But it has not yet been proved that the dendride processes are contractile enough as to lose all connections with the neighborly cells.