Amphimixis

“ Now when a Person throws a Stone into Water, these Undulations or Waves are raised in the Fluid for some Distance, by the Force and Action of one Wave upon another. This is the Case with regard to Sound; only the Air being an elastic Fluid, these Undulations are more quick and brisk in their Motions than in Water. So much for Sound itself. Now for the Cause of this Sound, or of these Undulations.
These Undulations are caused by the Vibration of some elastic Body, which is put into Motion by a Stroke of another Body against it. ”

“ When separated, there disengages itself from them a species of fluid of which the earth is the conductor, which develops and unrolls, so to speak, like the almost invisible thread of the spider, or that of the silk worm, which can be uncoiled and prolonged almost indefinitely in space without its breaking, but with this vital difference that the thread of the escargotic fluid is invisible as completely and the pulsation along it is as rapid as the electric fluid. ”

“ The temporary motion of a paralytic limb is likewise caused by passing the electric shock through it; which would seem to indicate some analogy between the electric fluid, and the nervous fluid, which is seperated from the blood by the brain, and thence diffused along the nerves for the purposes of motion and sensation. It probably destroys life by its sudden expansion of the nerves or fibres of the brain; in the same manner as it fuses metals and splinters wood or stone, and removes the atmosphere, when it passes from one object to another in a dense state. ”

“ If there is a long movement there will be a strong current and vice versa. If a sound is uttered, and even if the multitude of sounds that are required to form a word, be spoken to the diaphragm, the latter partakes in kind of the air-motions that strike it. It swings or vibrates in the air, and if it is a perfect diaphragm it moves exactly as the air does, both as to amplitude and complexity of movement. ”

“ This increase of number of pulsations from the recess-play is by no means the full measure of the benefit derived, for that increase implies a more rapid flow of the fluid through the hemal channels, and when we know that the carrying power of fluid currents increases as the sixth power of their velocities, we can appreciate with how much greater force these currents sweep through their courses, washing away the ashes, which have been made by previous combustion, from the brain-hearth and the muscle-hearth. ”

“ We can discriminate many more degrees of pitch than the 20,000 hair-cells, more or less, will allow for.
The so-called Fusion of Sensations in Hearing.—A very common way of explaining the fact that waves which singly give no feeling of pitch give one when recurrent, is to say that their several sensations fuse into a compound sensation. A preferable explanation is that which follows the analogy of muscular contraction. If electric shocks are sent into a frog's sciatic nerve at slow intervals, the muscle which the nerve supplies will give a series of distinct twitches, one for each shock. ”

“ Superposition of stimuli.—If instead of a single stimulus a succession of stimuli be superposed, it happens that a second shock is received before recovery from the first has taken place. Individual effects will then become more or less fused. When the frequency is sufficiently increased, the intermittent effects are fused, and we find an almost unbroken curve. When for example the muscle attains its maximum contraction (corresponding to the frequency and strength of stimuli) it is thrown into a state of complete tetanus, in which it appears to be held rigid. ”

“ In the inner ear of all animals are the so-called semicircular canals, which are provided with membranous walls, and are filled with liquid. At the end of each of these canals is an enlargement known as an ampulla, upon which is a delicate expansion of nerve-tissue derived from the nerve of hearing. These semicircular canals are so placed that every motion of the head must produce disturbance of the liquid contents of at least one of them, and consequently alterations of pressure on the nervous tissue in the ampulla. ”

“ The diaphragm serves but to increase the intensity of these effects, as in the transmitter, by concentrating the lines of force of the field, and by presenting a greater surface to the air—the necessary vehicle of sound. When it is thick, the internal motions that it takes on in consequence of variations in the field, and which are transmitted to the surrounding air and the ear, are solely those of resonance. ”

“ When we recollect, that the electric fluid itself is actually accumulated and given out voluntarily by the torpedo and the gymnotus electricus, that an electric shock will frequently stimulate into motion a paralytic limb, and lastly that it needs no perceptible tubes to convey it, this opinion seems not without probability; and the singular figure of the brain and nervous system seems well adapted to distribute it over every part of the body. ”

“ The air within each chamber remains under compression, as long as the siphuncle continues distended by the pericardia fluid; and returning, by its elasticity, to its former state, as soon as the pressure of the arms and body is withdrawn from the pericardium, forces the fluid back again into the cavity of this organ; and thus the shell, diminished as to its specific gravity, has a tendency to rise. ”

“ When the stimuli are sufficiently strong and follow each other with great rapidity, or when a strong continuous current is passed through the muscles, they are brought into a state of continuous contraction or tetanus, and in this condition they will remain for a long period or until the electric stimulus is removed. In cases where a severe electric shock is received as from an electric wire, the muscles which come in contact with the wire immediately contract and remain contracted while the current continues to pass through them. ”

“ The box has two pipes connected with it, by means of which it can be filled with carbonic acid gas.
Provided with this apparatus, it is now possible to show you a series of experiments which will leave no doubt in your minds that the external agency which creates in us the sensation of sound is a wave-motion in the air we breathe. Let me, in the first place, show you that a sound-beam can be reflected. We adjust our sensitive flame and set the whistle in action, and create, as described, by the lens, a beam of sound. ”

“ Deviations from the normal in the position or force of the apex beat will afford important information as to the nature of the pathological changes in the heart. Thus, displacement downwards and outwards of the apex beat, with a forcible thrusting impulse, will indicate hypertrophy, or increase of the muscular wall and increased driving power of the left ventricle, whereas a similar displacement with a feeble diffuse impulse will indicate dilatation, or over-distension of its cavity from stretching of the walls. ”

“ Stimulus of torsional vibration.—I find that torsional vibration affords a very effective method of stimulation. The plant-stalk may be fixed at one end, the other end being held in a tube provided with clamping jaws, A rapid torsional to-and-fro vibration can now be imparted to the stalk by means of the handle H. The amplitude of vibration, which determines the intensity of stimulus, can be accurately measured by means of a graduated circle. ”

“ The lips, vibrating as the breath passes through the aperture between them, communicate pulsations or series of intermittent shocks to the thin stream of air, known as the exciting current, which, issuing from them, strikes the column of air in the tube, already in a state of stationary vibration.9 The effect of this series of shocks, without which there can be no sound, upon the column of air confined within the walls of the tube is to produce sound-waves, travelling longitudinally through the tube. ”

“ In the disturbed regions we may generally remark a tract of limited extent in which the movement is particularly energetic. It corresponds, without doubt, with the deep-seated center of impulsion, and has been called the epicenter. Here is where the vertical shocks or succussions are most usually felt. From these radiate the undulatory movements, the speed of propagation of which has been estimated at from 1,100 to 1,500 feet per second, or about that of sound in the air. Sometimes the area of disturbance is very limited, even when the convulsion is most violent ”

“ This sound is produced by all muscles when in the state of contraction, the pitch of the note being not far from thirty vibrations per second. It is evidently only the intermittent discharge of the muscular fiber. A single excitation produces a muscular shock. As this production requires from eight to ten hundredths of a second, it is evident that, if another stimulus be applied before the first has disappeared, the two will coalesce; and when twenty per second reach the muscle it becomes permanently contracted or tetanized. ”

“ If a membrane of any kind is stretched across a hoop, and one talks against it, so to speak, the diaphragm or membrane will be shaken, will vibrate, with the movement of the air produced by the voice. If a cannon be fired all the windows rattle, and are often broken. A peal of thunder will cause the same jar and rattle of window panes, manifestly by what we call "sound"--vibrations of the air. The window frame is a "diaphragm." ”

“ Testing stimulus of sub-maximal intensity is applied at the middle of the nerve, where the constant current induces no variation of ex­cit­abil­ity. Stimulation is effected either by single break-shock or by the summated effects of a definite number of equi-alternating shocks, or by chemical stimulation
Experiment 45.—Under the action of feeble heterodromous current the transmitted excitation was always enhanced, whatever be the form of stimulation. ”

“ Hence we may conceive, that a very complex set of vibrations, arising from the mixture and combinations of degree, kind, place, and line of direction, exists always in the medullary substance, being kept up by its heat, and the pulsation of its arteries, when other causes are wanting, almost in the same manner as in a concert of music the air is agitated by vibrations of a very complex kind. ”

“ Thus dilute hydrochloric acid or ammonia causes excitation of both muscle and pulvinus. 3. Thermal.—The application of a hot wire will induce responsive contraction in both cases. 4. Electrical.—The muscle may be excited by an induction-shock. The pulvinus of Mimosa is also excited by such shocks. Other modes of electrical stimulation, such as that of condenser-discharge and that of the application of a constant electrical current, are found effective in causing excitation of animal tissues. ”

“ Every one is aware of the reinforcement of sound by the resonance of cavities. When singing or speaking near the aperture of a wide-mouthed vessel, the intensity of some one note in unison with the air in the cavity is often augmented to a great degree. Any vessel will resound if a body vibrating the natural note of the cavity be placed opposite to its orifice, and be large enough to cover it, or at least to set a large portion of the adjacent air in motion. ”

“ It will thus be seen, that external stimulus of electric shock induces a reaction which is of opposite sign to the normal growth elongation or expansion. We may conveniently describe this effect as ‘incipient’ contraction; for under increasing intensity of stimulus, the contractile reaction, opposing growth elongation, becomes more and more pronounced; at an intermediate stage this results in an arrest of growth; at the further stage, it culminates in an actual shortening of the organ. ”

“ But, if the rectangular shock be imparted to the pendulum when it is at the limit of its swing, then the compounding of the two impulses causes the suspended ball to describe, not a straight line, but an ellipse; and, if the shock be competent of itself to produce a vibration of the same amplitude as the first one, the ellipse becomes a circle.
Why do I dwell upon these things? Simply to make known to you the resemblance of these gross mechanical vibrations to the vibrations of light. I hold in my hand a plate of quartz cut from the crystal perpendicular to its axis. ”

“ Owing to the refractory period, the slow rate of contraction and the independence of the amplitude of contraction on the strength of stimulus, the heart under ordinary conditions cannot be thrown, by rapidly repeated excitation, into a complete state of tetanic spasm. ”

“ If the object to be assailed be sitting in a coffee-house, the pneumatic practitioner hovers about him, perhaps enters into conversation, and during such discourse, by opening the valve, sets at liberty the volatile magnetic fluid which is respired by the person intended to be assailed. So great is the attraction between the human body and this fluid, that the party becomes certainly impregnated, and is equally bound by the spell as the lady was fixed to the chair of Comus, or the harmless fly is enveloped in the shroud of the spider. ”

“ Numbness, being a diminution of sensibility, ought, according to the doctrine of vibrations, to proceed from such causes, as either indispose the parts for the reception of vivid vibrations, or hinder their free ascent to the brain. Agreeably to this, a compression made upon the nerve, which leads to any part, will occasion a numbness in that part, the nerve below the compression being unfitted thereby to receive vibrations freely, and the nerve above incapable of transmitting freely such as are excited. ”