John Gray McKendrick

“ The intensity of pain depends on the degree of excitability of the sensory nerves, whilst its mas- siveness depends on the number of nerve fibres affected. The quality of the pain is probably produced by the kind of irritation of the nerve, as affected by the structure of the part and the greater or less continuance of severe pressure. Thus there are piercing, cutting, boring, burning, throbbing, pressing, gnawing, dull, and acute varieties of pain. Sometimes the excitability of the cutaneous nerves is so great that a breath of air or a delicate touch may give rise to suffering. ”

“ Again, as showing that our knowledge of the tactile field is precise, there is the well-known fact that when a piece of skin is transplanted from the forehead to the nose, in the operation for removing a deformity of the nose arising from lupus or other ulcerative disease, the patient feels the new nasal part as if it were his fore head, and he may have the curious sensation of a nasal instead of a frontal headache. ”

“ The insane frequently have subjective tastes, which are real to the patient, and frequently cause much distress. In such cases, the sensation is excited by changes in the taste-centres of the brain. Increase in the sense of taste is called hypergeusia, diminution of it hypogeusia, and its entire loss ageusia. Rare cases occur where there is a subjective taste not associated with insanity nor with the circulation of any known sweetish matters in the blood, possibly caused by irritation of the gustatory nerves or by changes in the nerve centres. ”

“ Taste is often associated with smell, giving rise to a sensation of flavour, and we are frequently in the habit of confounding the one sensation with the other. Chloroform excites taste alone, whilst garlic, asafœtida, and vanilla excite only smell. ”

“ By touching a body at various points, from the difference of pressure and from a comparison of the positions of various points in the tactile field we judge of the configuration of the body. A number of " tactile pictures " are obtained by pass ing the skin over the touched body, and the shape of the body is further determined by a knowledge of the muscular movements necessary to bring the cutaneous surface into contact with different portions of it. If there is abnormal displacement of position, a false conception may arise as to the shape of the body. ”

“ In these circumstances the one cannot be distinguished from the other when the nose is firmly closed. No doubt also experience aids in detecting slight differences of taste by suggesting to the mind what may be expected; it is not easy, for instance, to distinguish the tastes of red and white wine when the eyes are blindfolded. ”

“ Taste may be educated to a remarkable extent; and careful observation—along with the practice of avoiding all substances having a very pronounced taste or having an irritating effect—enables tea-tasters and wine-tasters to detect slight differences of taste, more especially when combined with odour so as to produce flavour, which would be quite inappreciable to an ordinary palate. ”

“ Muscular Sense.—The sensory impressions considered in this article are closely related to the so-called muscular sense, or that sense or feeling by which we are aware of the state of the muscles of a limb as regards contraction or relaxation. Some have held that the muscular sense is really due to greater or less stretching of the skin and therefore to irritation of the nerves of that organ. ”

“ If the points of the compasses are unequally heated, the sensation of two contacts becomes confused. An anaemic condition, or a state of venous con gestion, or the application of cold, or violent stretching of the skin, or the use of such substances as atropine, daturin, morphia, strychnine, alcohol, bromide of potassium, cannabin, and hydrate of chloral blunt sensibility. The only active substance said to increase it is caffein. Absolute sensitiveness, as indicated by a sense of pressure, has been determined by various methods. ”

“ If we consider our mental condition as regards sensation at any moment, we notice numerous sensations more or less definite, not referred directly to the surface, nor to external objects, such as a feeling of general comfort, free or im peded breathing, hunger, thirst, malaise, horror, fatigue, and pain. ”

“ Further, cases in the human being have been noticed where there was an entire loss of cutaneous sensibility whilst the muscular sense was unimpaired. It is also known that muscles possess sensory nerves, giving rise, in certain circumstances, to fatigue, and, when strongly irritated, to the pain of cramp. Muscular sensations are really excited by irritation of sensory nerves passing from the muscles themselves. ”

“ The Amphibia and Reptilia do not show any special organs of touch. The lips of tadpoles have tactile papillae. Some snakes have a pair of tentacles on the snout, but the tongue is probably the chief organ of touch in most serpents and lizards. All reptiles possessing climbing powers have the sense of touch highly developed in the feet. ”

“ In the great majority of fishes touch is limited to the lips, to parts of the fins, and to special organs called barbels. In the Cyprinoids there is a fold of skin bordering the mouth which is highly tactile. The lip of the sturgeon is covered with numerous papillae; the sucking lip of the lamprey is papillose and highly sensitive. The fins are in many fishes modified to serve as organs of touch. ”

“ Similar bodies have been found in the epidermis of man and mammals, in the outer root-sheath of tactile hairs or feelers. They consist of small bodies composed of a capsule enclosing two or more flattened nucleated cells, piled in a row. Each corpuscle is separated from the others by a transparent protoplasmic disk. Nerve fibres terminate either in the cells (Merkel) or in the protoplasmic intercellular matter (Ranvier, Hesse, Izquierdo) . Another form of end-organ has been described by Herbst as existing in the mucous membrane of the duck's tongue. ”

“ The posterior part of its surface, where there is a Λ-shaped group of large papillæ, called circumvallate papillæ, supplied by the glosso-pharyngeal nerve, and the tip and margins of the tongue, covered with filiform (touch) papillæ and fungiform papillæ, are the chief localities where taste is manifested, but it also exists in the glosso-palatine arch and the lateral part of the soft palate. The middle of the tongue and the surface of the hard palate are devoid of taste. ”

“ Bats have the sense of touch strongly developed in the wings and external ears, and in some species in the flaps of skin found near the nose. These "nose-leaves" and expanded ears frequently show vibratile movements, like the antennae of insects, enabling the animal to detect slight atmospheric impulses. ”

“ Such animals, however, have broad, massive sensations of touch, enabling them to appreciate the firmness of the soil on which they tread, and under the hoof we find highly vascular and sensitive lamellle or papillte, contributing no doubt, not only to the growth of the hoof, but also to its sensitiveness. ”

“ End-Organs of Touch in Man.—In man three special forms of tactile end-organs have been described, and can be readily demonstrated.
(1) The End-Bulbs of Krause.—These are oval or rounded bodies, from 1/360 to 1/170 of an inch long. Each consists of a delicate capsule, composed of nucleated connective tissue enclosing numerous minute cells. On tracing the nerve fibre, it is found that the nerve sheath is continuous with the capsule, whilst the axis cylinder of the nerve divides into branches which lose themselves among the cells. ”

“ We are thus made conscious of whether or not the muscles are contracted, and of the amount of contraction necessary to overcome resistance, and this knowledge enables us to judge of the amount of voluntary impulse. ”

“ Wundt has propounded a psycho-physiological theory that every part of the skin with tactile sensibility always conveys an impres sion of the locality of the sensation. Each area of skin has a " local colour," and this diminishes from area to area. The grada tion is sudden where the sense of locality is acute and gradual where it is obtuse. " A circle of sensation is an area where the local colour changes so little that two separate impressions fuse into one " (Landois) . ”

“ Each corpuscle consists of 40 to 50 lamellae or coats, like the folds of an onion, thinner and closer to gether on approaching the centre. Each lamella is formed of an elastic material mixed with delicate con nective tissue fibres, and the inner surface of each is lined by a single continuous layer of endothelial cells. A double-contoured nerve fibre passes to each. ”

“ The same temperature applied to a large area is not appreciated in the same way as when applied to a small one ; thus " the whole hand when placed in water at 29 5 C. feels warmer than when a finger is dipped into water at 32 C. There is every reason to hold that there are different nerve fibres and different central organs for the tactile and thermal sensations, but nothing definite is known. The one sensation undoubtedly affects the other. ”

“ The greatest acuteuess is on the forehead, temples, and back of the hand and forearm, which detect a pressure of 002 gramme; fingers detect 005 to 015 gramme; the chin, abdomen, and nose 04 to 05 gramme. (2) Goltz s method gives the same general results as Weber s experiment with the compasses, with the exception that the tip of the tongue has its sensation of pressure much lower in the scale than its sensation of touch. ”

“ Sensitiveness to the movements of the ambient ocean is indicated by certain observed phenomena. The whale-fishers aver that when a straggler is attacked its fellows will bear down from some miles distance, as if to its assistance ”

“ If two different temperatures are applied side by side and simultaneously, the impressions often fuse, especially if the areas are close together. (4) Practice is said to improve the thermal sense. (5) Sensations of heat and cold may curiously alternate ”