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M. L. H. Arnold Snow, M.D. 1912 Chapter 10 Relation of Mechanical Vibration to the Nervous Systems
THE TWO GREAT SYSTEMS are the cerebro-spinal consisting of the brain, spinal cord, and cranial and spinal nerves, - and the sympathetic, consisting of a connected chain of ganglia on each side of the spinal column, three plexuses, - cardiac, solar, and hypogastric, which consist of nerves and ganglia "in front of the spine in the thoracic, abdominal and pelvic cavities respectively," and of smaller ganglia in relation with certain viscera, and two kinds of nerve-fibres, - communicating and distributary. A THIRD SYSTEM, the adrenal system, is recognized by Sajous and his followers. Three views [Landois. Text-Book of Human Physiology, page 621] are held regarding nerve elements. One view is that the "independent physiological unit of nervous tissue" is the neuron consisting of "a ganglionic cell with all of its processes. The axis cylinders of all nerve fibres arise from ganglionic cells and not from a network of fibres. All nerve fibres terminate finally by means of terminal arborescences or telodendrites. The nerve cells act as physiological centers for automatic or reflex movement, for sensation, perception, for trophic and secretory functions, and the fibres represent a conducting apparatus." A second view considers "the fibrillary substance or the neuropile as the medium of nervous activity. The fibrillary substance is present in the great mass of gray matter, which represents a fine lacework or network of nerve fibrils. It can be seen further in the nerve cells and in the fibres passing off from them." The third view [Sajous. The Internal Secretions and the Principles of Medicine, page XI, Vol. II] holds that the nervous system consists of cells, (the neuron being "not a cell but an organ composed of many cells), developed and nourished by leucocyte-granulations and traversed by the oxygen-laden adrenoxidase, and that " the ground substance and Nissl granules of nerve-cell bodies and the myelin of their axis-cylinders or nerves are to the nerve-cell what the cytoplasm is to other tissue-cells. The neuro-fibrils, including those of the axis cylinders, are nerve capillaries through which the nerve-cells are supplied with oxygen-laden adrenoxidase" which they receive "from the general circulation through the intermediary of the ueuroglia fibres (also capillaries) and the neurogliacells which regulate the volume of plasma admitted into the fibres. The axis cylinders [Sajous. The Internal Secretions and the Principles of Medicine, page 927] are the extension in the nerve of the neurofibrils which enter the dendrites from above and form a mesh work in the cell body (the main cell of the neuron) and around its nucleus." Sajous thinks "that the myelin of nerves is a compound rich in phosphorus which, when in contact with the oxygen-laden adrenoxidase circulating through them, generates nerve-energy" and "that the ground-substance, the Nissl granules and the myelin in the cell-bodies of neurons and their dendrites, are also phosphorus-laden compounds which, when in contact with the adrenoxidase circulating through them, generate nerve-energy." NERVE FIBRES CLASSIFIED ACCORDING TO FUNCTIONS [Landois. Text-Book of Human Physiology, page 677] are: (1) Centrifugal: (a) motor, (b) secretary, (c) trophic. (2) Centripetal: (a) sensory, (b) nerves of special sense, (e) reflex or excito-motor nerves. (3) Intercentral nerves connecting ganglionic cells. What concerns us particularly is the NUTRITION of
the nerve as it is affected by various
The chromatic substance accumulates in the cells when not active, whereas activity induces its consumption. Vas [Starr. Organic Nervous Diseases] noted that a mild stimulation caused the cell to swell and clear up in the center, and Mann showed that functional activity of the cell is accompanied by an increase in the size due to inhibition of the lymph lying in the cavity about the cell, the cell at work filling up the cavity in which it lies. When activity goes on to the point of fatigue then a shrivelling of the cell begins, first in the nucleus then in the body." These changes were the result of various stimuli both electrical and mechanical as running." If a cell that has been stimulated be given sufficient rest, it will revive and resume its functional activity but it is necessary that the blood supply be perfect and that the blood contain the requisite nutrition. There may be an injury to the neuron of a character which cannot be repaired, which will lead to organic nervous disease. According to Dr. Starr bacteria as well as leucocytes may be found in the neuron body and its branches. Howell [Text-Book of Physiology, page 139] believes the energy to be derived from "a metabolism which consists essentially in the splitting and oxidation of the complex substance in the protoplasm of the cell." THE SPINAL CORD is supplied with blood vessels which are non-anastomosing terminal arteries. When an embolus occurs in such an artery "an area of softening" results. Some of the veins empty their contents eventually into the vena cava, and others into branches of the jugular. The spinal cord controls various voluntary and involuntary actions of the human body. Nerve centers for many of these functions have been discovered, but others are as yet unknown or are in doubt, some authorities claiming one and some another region to be the center for a certain act or impulse, and yet again in some instances experiments have been made on the lower animals resulting in the discovery of certain centers which have not as yet been verified in respect to main. Nerve centers are considered in Chapter VI, and specifically in connection with the consideration of various organs when their pathological states are discussed. THE TWO ROOTS OF THE SPINAL NERVES, ANTERIOR AND POSTERIOR, differ in function. The anterior roots [Landois. Text-Book of Human Physiology, page 717] supply centrifugal fibres to: "1. Striated muscles of the trunk and of the extremities under the control of the will. Every muscle receives its motor fibres from several anterior roots and not from a single root, while every root distributes fibres to a related group of muscles. "2. Motor fibres to a number of organs provided with unstriated muscle fibres as urinary bladder, the uterus, vasa deferential the skin. "3. Motor fibres for the unstriated muscles of the vessels, the vaso-motors. "4. Inhibitory fibres for the contraction of the vascular muscles (known only in part): vaso-dilators. "5. Secretory fibres for the sweat. "6. Trophic fibres for the tissues." The posterior roots supply sensory nerves to the skin and internal tissues except for the face and the anterior part and inner portions of the head. "They also contain tactile nerves for the cutaneous surfaces indicated and can convey" irritations exciting reflex action. Stimulation of the anterior roots [Brubaker. A Compend of Human Physiology] causes: 1. Convulsive movements of muscles. 2. The formation of a secretion in glands. 3. Changes in the calibre of blood vessels. 4. Inhibition of the rhythmic activity of certain organs. Division of these roots is followed by: 1. Loss of muscular movement (paralysis of motion). 2. Cessation of secretion. 3. Cessation of vascular changes. Stimulation of posterior roots causes: 1. Reflex activities. 2. Conscious sensations. 3. Inhibition of the rhythmic activity of certain organs. Division of the posterior roots is followed by: 1. Loss of reflex activities. 2. Loss of sensation in all parts to which they are distributed. Sajous' [The Internal Secretions and the Principles of Medicine, page page XI, Vol. II] view in regard to the spinal system supported by evidence is embodied in: "That the pituitary body is the general and governing center of the spinal system, which includes the gray substance of the base of the brain, pons, bulb and spinal cord, and the nerves derived from any of these structures, cranial or spinal, though subsidiary centers are also present in the bulb and spinal cord." THE SYMPATHETIC SYSTEM is composed of three cervical, eleven dorsal, four lumbar and four sacral ganglia, and two [Landois. Text-Book of Human Physiology, page 718], kinds of fibres (1) medullated supplied to it as visceral branches by cerebral and spinal nerves, (2) fibres of Remak which arise from sympathetic ganglia," the medullated fibres being " (a) sensory; (b) motor for vessels (vasomotors) and viscera, the latter entering into sympathetic ganglia whence Remak's fibres, as well as medullated fibres, pass from the ganglion-cells to the innervated areas; (c) inhibitory fibres and vaso-dilators, in the course of which no sympathetic ganglia are intercalated. The situation of the ganglia [Belousow. Krause. Synoptic Charts of the Nerves of Man] varies in their relation to the vertebrae in the different regions. The superior cervical ganglion "is situated in front of the longus capitis muscle and the transverse processes of the 2nd and 3rd cervical vertebrae. (Gray says that sometimes it extends as low as the 4th or 5th.) It sends three or four rami communicantes to the anterior divisions of I to III cervical nerves, a communicating branch to ganglion nodosum of vagus nerve, a communicating branch to the hypoglossal nerve, the jugular nerve, the internal carotid nerve." The last three branches come from the upper part of the ganglion. The following are from the lower part of the ganglion. The external carotid nerves, pharangeal branches, laryngeal branches, and superior cardiac nerve. The superior cervical ganglion connects with the middle cervical ganglion and from this connection a branch is sent "to the anterior division of the fourth cervical .nerve." Anteriorly the superior cervical ganglion is " internal to the sterno mastoid high up." The middle cervical ganglion "lies at the level of the 5th or 6th cervical vertebra." It gives off the middle cardiac nerve, and "communicating branches to the anterior divisions of the 5th, 6th and 7th cervical nerves." Two trunks connect it to the inferior cervical ganglion. Anteriorly this ganglion is found "behind the middle of the sterno mastoid." The inferior cervical ganglion "lies at a slightly lower level than the middle cervical ganglion." (Gray says: "between the base of the transverse process of the last cervical vertebra and the neck of the first rib.") "It sends communicating branches to the anterior divisions of the 8th cervical and 1st dorsal nerves." (Gray states 7th and 8th cervical.) The inferior cardiac nerve, entering into the formation of the cardiac plexus, arises "from the inferior cervical and first thoracic ganglia." Other branches form the subclavian plexus of which "the inferior thyroid and vertebral plexus are the largest." The thoracic ganglia number ten, eleven, or twelve. The first and second thoracic are usually as one; and when these two are with the inferior cervical ganglion, the number of the thoracic ganglia is reduced to ten. Most of the thoracic ganglia "lie in front of the necks of the corresponding ribs. In the middle portion of the thorax they are slightly more external, in front of the transverse processes. Lower down they lie closer to the bodies of the vertebrae. They may be situated nearer the upper border, or nearer the lower border of the ribs, or in the intercostal spaces." The "greater splanchnic nerve comes from the 6th to the 9th thoracic ganglia. The roots pass in front of the bodies of, the dorsal vertebrae. The smaller splanchnic nerve comes from the 9th to the llth thoracic ganglia." The lumbar ganglia "lie on the bodies of the lumbar vertebrae." They usually number five. The sacral ganglia of which there are four,
or three, lie on the anterior surface of the sacrum,
The coccygeal ganglion "lies in front of the anterior surface of the second piece of the coecyx." The hypogastric plexus lies "in front of the
body of the fifth lumbar vertebra, and of the
Sajous states that the sympathetic system ("general motor system") has its governing center in the posterior pituitary body and that it is structurally a part of the general cerebro-spinal system. He believes that the function of the "sympathetic system [Sajous. The Internal Secretions and the Principles of Medicine, pages 294 and 1198] is to transmit efferent impulses and is purely vaso-constrictor, its field being limited to the small arteries or arterioles, and that it is independent of the vaso-motor system (whose action is general) being capable, unlike the latter, of influencing each organ individually, and that its terminals form part of the mechanism of all organs, and that the specific role of its terminal fibres is to oppose the strictodilators and restore the arterioles of an organ to their normal calibre when the functional activity of that organ is to cease. His conclusions [Sajous. The Internal Secretions and the Principles of Medicine, page 294] in regard to the study of the nerve supply of the voluntary muscles, the salivary, mammary, and cutaneous glands are as follows: "The general motor nerves distributed to the organs above mentioned divide, when near their destination, into two branches: (1) an 'extrinsic vasoconstrictor' branch, which supplies filaments to the arteries outside the contractile or secretary - structures of the organ concerned, and increases the speed of the blood-flow through the latter during activity by reducing the calibre of these arteries; (2) an 'excito-regulator' branch, which supplies the intrinsic structures of the organ and governs their functional activity, and which in turn divides into (a) an excitor and (b) an intrinsic constrictor branch." "As the vibratory rhythm of the stream of impulses transmitted by a nerve always corresponds with that of the structures to which its terminal filaments are distributed, any variation of vibratory rhythm transmitted from the cerebro-spinal centers by the general motor nerves gives rise to a corresponding variation of activity in the structures or organs supplied by these terminal filaments. "In all the above-mentioned organs the oxidizing substances combination of adrenal secretion and oxygen formed in the lungs and of which the blood plasma is the vehicle - is the physico-chemical agency through which cellular metabolism is sustained during passive functional activity, and increased during active functional activity." He states also "that the volume of blood which circulates through any organ, whether the latter be in the passive state or functionally active, is regulated by the joint action of the motor and sympathetic centers in the posterior pituitary, and that the cranial and sympathetic filaments to the arterioles owing to the presence in the walls of the arterioles of spirally disposed muscles, endow these vessels with a special property; that of increasing the vis a tergo motion of the blood in order to overcome the resistance of the capillaries." THE FUNCTIONS OF THE SYMPATHETIC SYSTEM according to Hall [Sajous. The Internal Secretions and the Principles of Medicine, page 1185] are: "1. Cardio-acceleration and cardio-augmentation through the branches from the cervical ganglia.. "2. Secretory impulses to the salivary glands, the stomach, the pancreas, the liver, the small intestine, the large intestine, the kidneys. "3. Vaso-motor impulses, both constrictor and dilator to all arteries and arterioles. "4. Motor impulses to the muscular coats of the stomach
and intestines, causing peristalsis and
"5. Motor impulses to the muscularis mucosa of the
alimentary canal, causing movements of the
"6. Inhibition. A THIRD SYSTEM is the "ADRENAL SYSTEM" which includes "the pituitary body, the adrenals and the thyroid gland including the parathyroids." Sajous' explanation is: "That the anterior pituitary body is a lymphoid organ which, through the intermediary of a center located in the posterior pituitary body and a nerve path in the spinal system, the upper dorsal sympathetic ganglia and the splanchnic nerves, governs the functional activity of the adrenals. "The anterior pituitary body governs, through the posterior pituitary body, all the oxidation processes of the body. The center in the posterior pituitary body through which the anterior pituitary body governs the adrenals also controls the functional activity of the thyroid gland, and thus constitutes the 'adreno-thyroid' center; which is governed by the test organ (the sensory organ between the two lobes of the pituitary body). The adrenal system is "the immunizing apparatus of the body" and its principal function is to supply an internal secretion which absorbs the oxygen of the air to carry it to the tissues. It is the system [Sajous. The Internal Secretions and the Principles of Medicine, page 231] through which cardiac action, respiration and general cellular oxidation are maintained. The processes governed by the posterior pituitary body "include all functions which require conscious and to a certain extent intelligent co-operation, and are, not mere reflex phenomena as those elicited from subsidiary nerve centers, in the medulla and spinal cord." THE VASO-MOTOR CENTER supplying motor fibres to the arterial muscles is thought by Landois to be in the medulla oblongata. This center may be stimulated directly or reflexly. "In animals in which the center is irritated electrically it has been found that single induction shocks of moderate strength are effective only when two or three shocks occur in a second. There is thus a summation of the effects of the individual stimuli." Ten or twelve strong or twenty to twenty-five moderately strong shocks per second induce the maximum vaso-constrictor effects shown by the maximum blood pressure. "THE VASO-MOTOR NERVES pass from their center in part directly [Landois. The Text-Book of Human Physiology, page 763] through the tract of some of the cerebral nerves to their distribution: - through the trigeminus in part to the interior of the eye, through the hypoglossus to the tongue, through fibres of the vagus to the heart and in limited number to the lungs and to the intestines. All other vaso-motor nerves descend in the spinal cord and are connected within the gray matter with centers of subordinate significance by means of contact. They make their exit, through the anterior roots of the spinal nerves, then pass through the visceral branches into the ganglia of the sympathetic cord. In the sympathetic cord they pass upward or downward and finally hence either to the vascular plexuses or through other visceral branches again into the trunks of spinal or cerebral nerves and from these to the respective vessels." According to Sajous' [The Internal Secretions and the Principles of Medicine, page 458] view "each general motor nerve distributed to a part supplies it with its vaso-motor fibres as well as with all others distributed to it, unless associated with a special nerve, such as the vagus," and consequently he concludes "that the vaso-motor center in the medulla must coincidently be that of the general motor nerves or at least the region where the latter assume vaso-motor functions." He concludes [Sajous. The Internal Secretions and the Principles of Medicine, page 463] that there is no individual center in the medulla to be called "vaso-motor center" and says "the general vaso-dilation after section of the medulla is due to the interruption of the stream of general motor impulses through which tonic contraction of the arteries is maintained, and which the medulla seems to transmit." He thinks the vaso-motors for the arterioles are from the sympathetic system under control of the sympathetic center and that the larger vessels are controlled by the bulbar vaso-motor center. THE VASO-DILATOR NERVES or vaso-inhibitory nerves
or vaso-hypotonic nerves should be further investigated. Some authorities
(Landois) believe that they exist as special nerves or associated with
vaso-constrictor and other nerves. Sajous states that the functions
of vaso-constrictor and vaso-dilator nerves of muscles are filled "through
the agency of their motor nerves," and that "stricto-dilators "which are
fibres of a cranial motor or secretary nerve (the vagus, facial, etc.),
cause dilation of an arteriole during functional activity, and that the
vaso-constrictor fibres of the sympathetic (whose control is united to
arterioles or small arteries) restore a passive condition. He also
believes that "active vaso-dilation exercised through
Stimulation of PRESSOR and DEPRESSOR fibres of "different afferent nerves" excites or inhibits the action of the vaso-motors. Loven believes that "the first effect of stimulating every sensory nerve is a pressor action" and "S. Mayer and Pribram found that mechanical stimulation of the stomach, especially of its serosa, caused pressor effects." Sajous thinks "the depressor nerves are those through which the thyroid center regulates the circulation of the anterior pituitary body and of the thyroid apparatus." THE VASO-MOTORS TO THE HEAD ARE MOSTLY FROM the cervical sympathetic, to the upper extremities "through the anterior roots of the middle dorsal nerves, into the thoracic sympathetic, and upwards to the last thoracic ganglion, and from thence to the rami communicantes to the brachial plexus (Schiff, Cyon)," to the lower extremities "through the nerves of the lumbar and sacral plexuses into the sympathetic, and from thence to the lower limbs (Pfluger, Schiff, Cl. Bernard)," to the skin of the trunk through the dorsal and lumbar nerves, to the lungs "from the dorsal spinal cord through the first thoracic ganglion (Brown-Sequard, Fick and Badoud, Lichtheim) to the abdominal viscera from the splanchnic" (v. Bezold, Ludwig and Cyon). [Landois and Stirling. Text-Book of Human Physiology, 4th ed., page 856] A light cutaneous stimulus lowers the cutaneous temperature, and lessens "the volume of the corresponding limb, and sometimes causes an increase of the general blood pressure and change of heart-beat." The body temperature and even the body weight are through stimulation of particular vascular areas acted upon by the vaso-motor nerves. Stimulation of a motor nerve or the spinal cord causes not only the contraction of the corresponding muscles, but also dilatation of their blood-vessels, (C. Ludwig and Sezelkow, Hafix and Gaskell) - the dilatation of the vessels taking place even when the muscle is prevented from shortening. Gaskell observed under the microscope the dilatation produced by stimulation of the nerve to the mylo-hyoid muscle of the frog. Some think that vaso-dilator fibres arise from all parts of the spinal cord, the ear receiving its supply from the lowest cervical ganglion and first dorsal. The nervi erigentes from the sacral plexus when stimulated cause the arteries of the penis to dilate. (Eckhardt, Loven.) [Landois and Stirling. Text-Book of Human Physiology, page 863] In applying mechanical vibration take as a guide the rule, " Stimuli, which are applied at long intervals to the nerve, act especially on the vaso-dilator fibres, while tetanizing stimuli act on the vaso-motors (constrictors). The latent period of the vaso-dilators is longer and they are more easily exhausted than the vaso-motors (Bowditch and Warren)." MECHANICAL VIBRATION WHEN APPLIED TO AN INFLAMED NERVE elicits pain if a sensory nerve or contraction if a motor nerve which may at first be increased or exaggerated. Prolonged application results in diminution or disappearance of the pain or contraction. It is of interest to note Tigerstedt's findings. "Tigerstedt [Landois. Text-Book of Human Physiology, page 629] discovered that the minimal value of the mechanical stimulation (induced by the falling of a weight upon the isolated nerve) is 900 milligram-millimeters, the maximal value from 7000 to 8000. More powerful stimulation causes exhaustion, but this does not extend beyond the irritated area. The mechanically irritated nerve does not acquire an acid reaction. A lesser degree of pressure or tension increases the irritability, which again diminishes after a short time. The work done by the irritated muscle as a result of this irritation was as much as 100 times greater than the kinetic energy of the mechanical nerve irritation. If a mechanical influence acts gradually the nerve may lose its conductivity or its irritability without any manifestation of irritation in the process." Heidenhain's tetanomotor, a vibratory apparatus, is used in investigation work to cause nerve stimulation mechanically. It will induce "a tetanus lasting up to two minutes. Spinal cord stimulation may be from interrupted vibration or peripheral nerve stimulation frictionally. Peripheral stimulation results from local vibrations with the disc vibratode. Stimulation or inhibition may result according to the length of time and degree of pressure exerted. The heart may be slowed or quickened by nerve vibration. It has been demonstrated that vibration from various devices [Cyriax. Vibrations and Their Effects] induced muscular contraction (Langendorff and Axenfeld), and stimulatory effects (Borruttau)." Bechterew and Tschigajew [Cyriax. Vibrations and Their Effects] by vibrating the whole body induced sleep in about 1/4 hour. Buchheim obtained stimulatory effects on the sympathetic and vagus in the neck according to the site of application." Nerve vibration reflexly affects the activity of organs. "Nebel, Lenmalm and others found that in some cases paralyzed nerves would react to mechanical (a vibratory nerve pressing) but not to electrical stimulus." Mechanical stimuli act when sufficiently rapid to cause a change in the nerve particles. Their effects vary: if the pressure on a mixed nerve be continuous the motor fibres are paralyzed sooner than the sensory. If the pressure be increased gradually an increase of excitability follows to be later followed by a decrease. According to Kroneeker and Zederbaum pressure applied to a mixed nerve abolishes reflex conduction before motor conduction. Fontana, 1758, found that a stimulus increased very gradually caused the nerve to be inexcitable without showing stimulation signs. A mechanical stimulus does not cause the nerve to become acid. When a motor nerve is irritated, the nearer the nerve center the greater the excitability, that is a muscle that contracts with a given stimulus at a given point will answer with a greater contraction if the same stimulus be applied nearer the spinal cord. Reflex contractions [Landois. Text-Book of Human Physiology, page 633] caused by irritating a sensory nerve "are the greater the more proximally the irritation is applied." Yet another point to b noted is that in the same nerve a stronger stimulus is required for it to act on some muscles as of extensors than on others as flexors, as has been demonstrated on the sciatic nerve of a frog. The facts set forth may ultimately aid in estimating the degree of stimulation indicated for various groups of muscles which it may be advisable to affect. If stimulation be continuous and excessive, fatigue followed by exhaustion results. Bernstein demonstrated that "a nerve trunk is more slowly fatigued than a muscle, but it recovers more slowly" [Landois and Stirling. Text-Book of Human Physiology, 4th ed., page 683] which suggests a judicious employment of vibratory stimulation according to the ease treated, that over stimulation be avoided. Nerves are capable of carrying impulses even after there is loss of excitability. We should not stimulate a nerve too rapidly in order that the nervous impulse may be allowed to travel without interruption. The impulse travels in a motor nerve at from "100 to 120 feet per second as found by v. Helmholtz and Baxt" and from 90 to 280 in sensory nerves, as shown by v. Helmholtz. It is less in the visceral nerves, being but 26 feet in some branches of the vagus (Chauveau). Reflexes are best induced by 16 stimuli per second. REFLEX ACTIVITY is considered by some authorities to be of great importance as it is believed that in chronic visceral diseases "the spinal muscles lying over the reflexly affected spinal nerve center will generally be found contracted, and if long coijtinued more or less atrophied, "and that stimuli" applied directly over the affected center," act as a vis a tergo to restore normal functionating power. Interrupted vibration with the ball used alternately on each side of the spine between the transverse processes is an effective stimulus. "Strong stimulation of a sensory nerve inhibits reflex movements. The reflex does not take place if an afferent be stimulated very powerfully (Goltz, Lewisson)." Setschenow distinguished tactile reflexes, which are discharged by stimulation of the nerves of touch; and pathic which are due to stimulation of sensory (pain conducting) fibres. He and Paschutin suppose that tactile reflexes are suppressed by voluntary impulses, and the pathic by the center in the optic lobes. Jendrassik makes the following subdivision of reflexes: [Landois. Text-Book of Human Physiology, page 731] "I. Spinal (tendinous, muscular, periosteal, bony, articular, genital-muscle). Pathologically manifested as flexor, less often extensor movement of the lower extremities. II. Cerebral cortical caused by tickling. III. Complex from a spinal and a cerebral reflex center, sneezing, vomiting, swallowing, coughing, evacuation of bladder, and rectum, and ejaculations." The following is of interest as regards reflexes: "1. Reflexes are more easily and more completely discharged when the specific end-organ of the afferent nerve is stimulated, than when the trunk of the nerve is stimulated in its course " (Marshall-Hall). 2. A stronger stimulus is required to discharge a reflex movement than "for the direct stimulation of motor nerves. 3. A movement produced reflexly is of shorter duration than the corresponding movement executed voluntarily. Further the occurrence of the movement after the moment of stimulation is distinctly delayed. In connection with the subject of reflexes the question arises whether the spinal cord is or is not stimulated when we stimulate the posterior root. "As the spinal cord conduces to the brain impulses communicated to it from the stimulated posterior roots, but does not itself respond to stimuli which produce sensations, Schiff has applied to it the term 'aesthesodie'." Further as the cord can conduct both voluntary and reflex motor impulses, without, however, itself being affected by motor impulses applied to it directly, he calls it "kinesodic." Many others believe that direct stimulation will excite the spinal cord. Reflex time or the time for carrying impulses by means of the afferent nerves through the cord to the efferent varies, in the frog being .0008 to .015 second, but is increased by "almost 1-3 if the impulses pass to the other side of the cord." It lessens as the strength of the stimulus is increased "and may even become of minimal duration." (J. Rosenthal.) What investigation has demonstrated of the relation that stimuli bear to effect has been aptly summarized by Kirke acording to Pfluger as follows: "l. Law of unilateral reflection. - A slight irritation of the surface supplied by certain sensory nerves is reflected along the motor nerves of the same region. Thus if the skin of a frog's foot be tickled on the right side, the right leg is drawn up. 2. Law of symmetrical reflection. - A stronger irritation is reflected, not only on one side, but also along the corresponding motor nerve of the opposite side. 3. Law of intensity. - In the above case, the contractions will be more violent on the side irritated, but it must not be assumed that the effect is always ,in proportion to the strength of the stimulus. 4. Law of radiation. - If the irritation (afferent impulses) increases it is reflected along other motor nerves till at length all the muscles of the body are thrown into action. The vagus nerve is particularly worthy of notice as it has such a wide range of control. "It supplies (1) motor influence to the pharynx and oesophagus, stomach and intestines, to the larynx, trachea, bronchi and lung; (2) sensory and in part (3) vaso-motor influences, to the same regions; (4) inhibitory influence to the heart; (5) inhibitory afferent impulses to the vaso-motor center; (6) excito-secretory in the salivary glands; (7) excito-motor in coughing, vomiting, etc." Scientific conclusions are of importance to all employing vibratory stimulation of whatever form - static wave current, high-frequency current, or mechanical vibration. They demonstrate the existence of factors that are too often overlooked. VIBRATORY FRICTION acts on nerve endings of both systems and interrupted vibration acts upon the nerve trunks and centers. Lightly applied, interrupted vibration stimulates while stronger or longer fatigues or exhausts the nerves, according to the degrees, and may affect the blood flow, causing a numbness from diminished nutrition. Percussion excites "languid" nerves, but if long and vigorous may over stimulate them and exhaust their ability of perceiving impressions and allay morbid irritability, a point of therapeutic interest. LIGHT PERCUSSION at first increases pain, but later diminishes it, often causing it to finally disappear. The greater the sensitiveness of the nerve, the less pressure should be at first employed. VIBRATORY STROKING has a soothing effect and vibratory friction by acting on the nerve of the blood vessels and lymphatics has a marked effect on inflammation. It also helps to give the tired nerves their necessary blood supply. WHEN DEEP INTERRUPTED VIBRATION, even compressing in character, is used pressure on the trunk is best made over the "motor points." Douglas Graham says "it is often surprising how much better contraction can be obtained from percussion than from a faradic current." When made on the solar plexus below the xiphoid cartilage and the lumbar ganglia, situated about two inches on each side of the umbilicus, the patient should exhale slowly and forcibly, breathing deeply. All abdominal viscera will be affected If deep interrupted vibration is applied to the aortic lumbar plexus the vibratode should be placed about two inches below the umbilicus. During applications to these regions the patient should lie on his back, the head and shoulders being elevated, the legs being flexed. The patient should breathe deeply and during forced exhalation the pressure should be increased, the vibratode being carried more deeply at the sites of application. Each impulse should be but for a few seconds at each site, the period of rest being as long or twice as long as the time of contact. The vibratodes should be applied but for three or r times and great care must be exercised that the re is not applied too suddenly or too heavily, as unpleasant effects, such as nausea and depression may result. Deep interrupted vibration with moderate or deep pressure is stimulating if the application is short, but is exhausting if too strong or if it be applied too long. In applying interrupted vibration to the spine place the ball vibratode over the site of the ganglion and make the pressure close to the spinous processes and between the transverse processes, or between the ribs near the spine. The "chief actions of the sympathetic nerves
on the one hand, and of the cranial and sacral autonomic nerves
on the other, in the regions of double supply" are as follows:
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