The Medium of Communication. - A masterful knowledge of nerve tissue and its arrangement in the body to form the nervous system is an absolute prerequisite for success in osteopathic practice.  Every vital phenomenon calls for interpretation by the skillful physician.  Interpretation cannot be attempted without a definite knowledge of structure and function of that tissue which acts as a medium of communication between all other elements of the body.

    The name of our system, Osteopathy, calls attention primarily to osseous structure, but it is only in connection with its effects on the tissues of communication and exchange, vital phenomena, we are actually interested.

    The Attributes of Nerve Tissue. - All physiological phenomena are characterized by the manifestation of attributes of nerve tissue, irritability, conductivity and trophicity.  Motion, sensation and nutrition are the vital phenomena whose perversion consulates disease.  Therefore, whatever the pathological condition may be, we are called upon to note a change in some one or all of these attributes of nerve tissue.

    Nerve and Muscle Irritability. - Scarcely any thought of muscle is ever complete without the nerve impulse which controls the muscle is also considered.  For convenience sake we may separate nerve and muscle when teaching their special attributes, but for all practical purposes they are never separated.  Muscle and nerve are both irritable, but we pay no attention to the irritability of muscle because under normal conditions we do not see any evidences of specific muscular irritability.  We view muscular irritability as the result of nerve irritability.  Therefore nerve tissue is the chief irritable tissue.  Irritability is an attribute of cell proto-plasm whereby chemical and physical phenomena are enacted in response to irritants.  Irritants may be mechanical, chemical, thermal and electrical.  Practically all that physiologists know of the reactions of nerve tissue to irritants has been derived through experimentation by means of the electrical current.  Osteopaths are bringing to light many facts concerning mechanical stimulation.  Hydrotherapists have demonstrated the utility of thermal stimuli.  Drug therapy makes use of the clerical form of stimulation.

    Conductivity. - Nerve tissue is not only irritable but possesses the ability to transmit its irritability to other tissues and cause certain activities to be initiated there.  Conductivity, the second vital attribute of nerve tissue, is the power to carry impulses from the point of irritation to other points in the nervous system.  Irritability would be of small moment if conductivity were not present to transmit the message to the center and arouse response.  The nerve cell and its axis-cylinder are a continuous mass of protoplasm and as long as the continuity is maintained conductivity will be maintained.

    Trophicity. - The third attribute of nerve tissue, trophicity, is very imperfectly understood.  We do not use this term here to represent so much the nutritional influences of the cell-body over its axis-cylinder as the influence exerted by nerve tissue over other body tissues, causing them to grow and prosper.  This nutritional influence over other tissues is an attribute which we are compelled to note quite frequently in practice.  There are individuals in whom motion and sensation are normal but nutrition fails, hence we note that in some cases mechanical lesions may cause only a slight change in the nerve tissue upon which they impinge, and this change is manifested by variation in nutrition of the part controlled by the irritated nerve.  It is probably this attribute of nerve tissue which is perverted or lost when the tissues refuse to take up certain chemical elements which are ordinarily normal to them; for example, iron.  In osteopathic practice we consider nutritional disorders as being the result of perverted trophic influence of nerves.  Of course in cases where it is known that the ingested food does not contain the required element or elements we must regulate the diet.  But there are many cases where all conditions appear normal, except that the tissues do not take up nourishment as they should.  In these cases we search for lesions in the same way we would if motion or sensation showed perversion or loss.  This phase of our subject can best be considered at another time.

    Unity of the Nervous System. - The unity of the nervous system is a physiological fact, and this brings deep and superficial areas in close relation.  Every portion of the body is able through the medium of the nervous system to work in harmony with every other part.  Physiologists divide the nervous system into central and peripheral portions, but for practical purposes this division is of little use to us when attempting to make use of the irritability and conductivity of the nervous system for therapeutic purposes.  Since all portions of the nervous system are connected there must be some place where impressions made upon terminal nerve filaments may be assembled, coordinated and responded to harmoniously.  Wherever large numbers of nerve cells are assembled we expect to find such duties performed.

    Other Systems of Integration. - Any influence which we have upon the body through therapeutic methods must be based on the unity of the body.  That the body is a unit must be constantly borne in mind, not only a unit because of the nervous system but also a mechanical unit, formed by its fibrous tissues and a chemical unit through its circulating media.  The nervous system is so preeminently the master tissue that, when we think of any integrative reaction, we attribute it to this tissue, which not only takes note of impressions secured by contact but reaches out into surrounding space and causes the body to react to things at a distance.

    Mechanical Irritation. - The particular therapeutic procedures with which we are here dealing are aimed to affect by contact and hence we are most interested in those reflexes originating through stimuli applied to skin, visceral and somatic tissues.  Structural displacements in the human body act as mechanical irritants to nerve tissue, changing the chemical and physical condition of the protoplasm and thus altering its irritability, either plus or minus according to the intensity of the stimulation.  The displaced structures may have other detrimental influences on nerve tissue, for instance the pressure brought to bear on the nourishing liquids surrounding the nerve, i. e., the blood and lymph, may cause sufficient chemical change in these liquids to materially affect irritability of the protoplasm of the nerves which they are expected to nourish.

    Effect on Conductivity. - Conductivity is not destroyed by these slight mechanical pressures.  If the protoplasm of the cell and axis-cylinder were unable to conduct impulses and project them in such manner as to reach other cell bodies of the nervous system our work would be very limited.  Conductivity depends on the continuity of protoplasm.  The mechanical irritations we deal with in osteopathic practice seldom destroy conductivity.  If they did so they would cease to become irritants the moment conductivity was lost.  Other irritants may act for a time oil the severed portions of protoplasm, but the original lesion would have destroyed the continuity of the protoplasm.

    Afferent and Efferent Fibers. - The fibers composing a nerve bundle may be efferent or afferent so far as direction of impulse is concerned.  Efferent fibers may be further differentiated by the names, motor, vasomotor, secretary, according to the structures in which they end.  Afferent fibers are usually termed sensory to denote their function of carrying impulses to the central nervous system.  Nerve trunks contain all of these various fibers, therefore, pressure will irritate all of the fibers and conductivity of individual fibers will transmit the impulses in the direction of the normal nerve impulse, thus causing contraction in the voluntary or involuntary muscles or activity of secretary tissues; sensory impulses will be transmitted to the central nervous system and will purport to come from the terminal distribution of the sensory nerve.  If the afferent impulse is such a one as will reach the patient’s consciousness, we find that the central cells are misled as to the location of the stimulus and hence manifest a response in the supposed area.  It is not necessary for the patient to be conscious of any irritation in order to bring about this result.

    Organization of the Nerve Bundle. - The organization of the nerve bundle complicates our ideas of irritability and conductivity in the protoplasm of the cell and axis-cylinder of a nervous unit.  Complexity of action and reaction increases as we near the central nervous system.  We have considered that all impulses generated in the protoplasm of a nerve cell and axis-cylinder have been transmitted to all parts of that unit of nerve tissue, but have not in any way influenced any other unit.  We have not considered the relations of cell bodies in the central system.  It is sufficient for our present purpose to note that the afferent fibers enter the spinal cord as the posterior roots and that their cells are in the ganglia of these posterior roots.

    Intraspinal Fibers. - The efferent fibers leave the cord as its anterior roots and their bodies are located in the anterior cornua of the gray matter of the cord.  Upon careful study of the spinal cord there are found other cells and axis cylinders which do not leave the cord but serve to connect the afferent and efferent elements and distribute impulses within the cord.  These latter are found in enormous numbers in all portions of the central nervous system.
 
    Segmentation of the Spinal Cord. - The first fact of great interest to us, osteopathically, is the segmentation of the spinal cord.  This is only relative in character, but yet is apparent, not only histologically but pathologically.  We note that according to distribution of afferent fibers in the spinal cord impulses are diffused both above and below the point of entrance.  The cell bodies of the anterior roots are also somewhat diffused, but in practice we note that afferent and efferent impulses seem to be correlated within comparatively narrow limits in the spinal cord.  How the impulses set up in the protoplasm of all afferent fiber are transmitted from it to the protoplasm of other cells located in the spinal cord and thence transmitted to the protoplasm of efferent cells is not known, nor is it necessary for us to thoroughly understand the method in this instance so long as we recognize the results.  Our specific knowledge must comprehend the exact point of entrance to and exit from the spinal cord of each nerve bundle and the peripheral distribution of the same.  Having a knowledge of the structure, the function comes naturally as a result.
 
    Segmental Integration. - A segment of the spinal cord, i.e., that portion giving rise to a pair of spinal nerves may be conceived to act independently of other segments.  Of course it would be difficult to demonstrate this, but for purposes of analysis we may be permitted to segregate the various divisions and nervous elements so as to better understand the structures with which we are dealing.  The central nervous system is constantly receiving impulses from afferent fibers and coordinating them.  We are almost entirely dependent on reflex action for the effects we secure on deep tissues.  Our manipulations affect sensory nerves in skin, muscle and synovial membranes.  These impulses are carried to the central nervous system and transformed into efferent impulses.
 
    Ceaseless Play of Reflexes. - During life there is no period when the body is not dependent on external stimuli.  These ordinary mechanical and thermal stimuli keep a constant stream of impulses entering the central system to be translated into stimuli of muscle and gland.  This ceaseless play of reflexes may vary in intensity, but so long as life lasts they are demonstrable.  We expect the reflex to be initiated by the sensory side of the reflex arc, therefore the intensity of muscular contraction and glandular secretion is governed by the intensity of the initiatory impulse.

    The Simple Reflex. - The simplest reaction in the nervous system may be conceived as a sensory impulse transmitted to the spinal cord over a sensory nerve and from the cord over a motor nerve.  The tissue in which the motor or efferent nerve ends will express reaction to the stimuli coming over the sensory or afferent side of this reflex arc.

    The Sensory Side of the Reflex Arc. - The sensory side of the reflex arc is the one upon which we must depend to initiate reactions.  The segment coordinates the sensory impulses reaching it over the afferent roots of its nerve trunks.  By following the distribution of its nerves we can determine what cells its afferent fibers arise in and what cells its efferent fibers innervate.  Taking a mid-dorsal segment we find its pair of nerve trunks dividing and branching so as to supply skin, muscle and viscera.  All of these parts must have sensory and motor fibers and since our spinal nerves are mixed nerves, i. e., have afferent and efferent fibers, we know that a segment receives sensory impulses from skin, muscle and viscera and the segment integrates these impulses and sends out efferent impulses coordinated for the best good of itself and the tissues it innervates.

    Protective Reactions. - A reflex is primarily a protective reaction.  It is an effort on the part of the structures entering into the reaction to protect that of which they are a part.  It seems that the sole object of a reflex is self defense.  Therefore a study of reflexes will tend to make symptomatology far more interesting.  The integration expressed in the reactions of a spinal segment mirror the manifold relations existing between the cells which constitute the active elements in a metamere or body segment.  The segmental structure of the cord and the reflex action manifested therein show that, on the whole, a definite muscle group and a definite cutaneous area are innervated from a limited portion of the central system.  Therefore we may count on the stimuli originated in the cutaneous area being reflexed to the definite muscular area.

    Example. - An example in practice is as follows: Patient's head is drawn slightly to the left side.  complains of pain shooting to the left shoulder and over the left clavicle whenever movement is attempted.  History of exposure to draught of cold air.  Physical examination discloses contraction of left trapezium, levator anguli scapulae and scaleni.  Pressure upon these muscles causes pain.  When instructed to take a full inspiration, patient says he cannot on account of pain, which is sharp and darting in character and radiates over the intraclavicular portion of the left chest.  When we consider the muscles involved and the area of painful sensations, our attention is immediately called to a definite segment of the cord, in this case the point of origin of the third and fourth cervical nerves.  'The cold air striking the skin intensified the normal stimuli and the efferent impulses from that segment of the cord were intensified as the direct result of the cutaneous irritation.  'The point of irritation, the cutaneous area, governed the location of the reflex.  So long as the original stimulus was only moderately intensified all the reflexes emanated from one segment of the cord, but if they had been more intense or continued longer, we might have found a greater area reflexly affected.  The stimuli which would have reached the cord would have been more widely diffused above and below the point of entrance.

    Comparative Segmentation. - Since we know that the highly organized spinal cord of man is not to be compared with the same structure in lower forms of animal life and that segmentation in it is illy defined, the practical question arises as to how much dependence we can put upon reflexes in the human nervous system.  Will the reflexes guide us to definite segments of the spinal cord?  Experience teaches us that a thorough knowledge of the distribution of afferent and efferent nerves in man will interpret reflexes with sufficient exactness and invariably lead the investigator to a spinal segment which is itself affected or is coordinating pulses from a known sensory area.

    Efferent Impulses. - When we follow the efferent impulses to their points of distribution our work is greatly complicated.  To reason from contracted voluntary muscle to cutaneous sensory area is a comparatively simple procedure, but to start with the sensory impulse and trace it through the central system and thence along efferent pathways, to estimate its final effects, as mechanical work done by muscle and gland in many combinations, requires a considerable knowledge of structure and function of all parts of the human system.

    Efferent Fibers to the Sympathetic Ganglia. - Many of the efferent fibers of the cerebro-spinal system take their course through the sympathetic ganglia and are distributed in that system to plain muscle and secretary cells of the body.  It has been ascertained by various careful observers that these efferent fillers, after entering the sympathetic system, either end in the ganglia nearest their point of emergence from the cord or pass up or down to ganglia above or below the one originally entered.  Some fibers pass through these ganglia and end in the more peripherally placed plexuses.

    Ganglionic Control. - Wherever nerve cells are accumulated a certain amount of independent action is probably carried on.  Terminal filaments of efferent fibers in sympathetic spinal ganglia are in relation with a large number of cells and the number of fibers leaving the ganglia is greater than those entering.  Therefore diffusion of impulses from these ganglia must be very great.  The accumulation of sensory impulses in these ganglia may be equally as great.  Each ganglion must have a dominant influence over a certain visceral area, and this influence is subsidiary to the control exercised by the segment of spinal cord to and from which the larger number of fibers proceed.
 
    Three Fields for Reception of Sensory Impressions. - The three original layers of the embryo, epiblast, endoblast and mesoblast, forming skin, mucous membrane and the intervening tissues, are represented by sensory fibers which connect them with the central nervous system.  The outer surface of the body is supplied with extero-ceptive, the internal surface with intero-ceptive and the intercellular surfaces with proprio-ceptive fibers.  The coordination of these various receptive fields is the duty of the segment.  We have reactions in this segment which represent the effort of the segment to adapt itself to external conditions.  The external surface registers in the segment the conditions of the outside world, so far as the special endings of its sensory nerves are capable.  The internal surface takes cognizance of the presence of material in contact with it which in most cases may serve as food.  Not all spinal segments have this visceral division represented in them.

    Proprio-ceptive Field. - The surface of the individual cells, which compose the bulk of the body, are represented in the segment by a large number of sensory fibers which register their conditions and needs.  This proprio-ceptive field is an exceedingly large one and is usually little thought of when considering the reactions of the nervous system.  It is the proprio-ceptive nerves which are affected in any trauma of joints or other deep structures.  The sense of position, muscular tension and weight are to a large extent dependent on these fibers.

    Segmental Coordination. - The segment of the spinal cord governing a metamere receives sensory stimuli from three different receptor fields, the external and internal surfaces and the bulk of the tissue between these surfaces.  The harmonious functioning of the whole segment is the result of the coordination of all the impulses from these three receptor fields, expressed in effector tissues, muscle and gland.  These reactions represent the segment’s effort to meet the conditions of its environment, plus its own inter-cellular condition, to the best advantage. In other words, its reactions represent its effort to maintain its existence.

    Plurisegmental Control. - Just as no skin area, or muscle, other than a distinctly segmental one, as mentioned in Chapter V, no viscus is wholly under the influence of one segment.  Therefore one segment is merely a contributor of a partial influence over skin, muscle and internal organ.  One segment may furnish the majority of fibers to a certain peripheral nerve, but complete control is divided between two or more segments.  This seems to indicate that physiological centers in the spinal cord consist of series of cells, placed vertically, whose fibers thus emerge at various levels.  With this fact in view we recognize that any reaction to stimuli, arising in any one of the three receptor fields, will be expressed in effector tissues belonging to at least two or more metameres.  Therefore any protective reaction in spinal areas will involve more than one spinal articulation.

    Clinical Evidence, Group Lesions. - This agrees with the clinical findings.  Take spinal tenderness for example: A point is usually found which shows considerable tenderness and this tenderness shades off through a metamere above and below the most sensitive point.  Contraction of a spinal muscle, i. e., of a portion of the erector spinae, extends over two or more metameres.  Osseous lesions are usually of the group character.  The approximation or separation of two spinous processes represents the involvement of at least four vertebrae, i. e., one above and one below the center of the lesion.  Likewise, the lateral deviation of a spinous process means the involvement of three vertebrae.  Thus we see that all reactions are practically pluri-segmental instead of segmental.  The vertical arrangement of the governing cells in the spinal cord is the foundation for this.  Just as we noted the migration of muscles for purposes of better guarding of the body, so also we note that segments have divided their influence with adjoining ones.
 
    Differentiation of Spinal Lesions. - In view of these facts it is hard, in fact impossible, to differentiate spinal lesions as primary or secondary, i. e., traumatic or reflex, based on palpation of the tissues.  The characteristics are quite similar because the protective reactions of the body, whether in response to stimuli from the extero-, intero-, or proprio-ceptive fields, will be manifested in the effector tissues, muscle and gland, of the pluri-segments belonging to the receptor fields receiving the stimuli.  For example: Irritation of the skin of the back supplied by nerves from the segments of the cord which have rami-communicantes connecting with the renal splanchnics, may produce reactions in all the tissues governed by that pluri-segmental center.  A stream of cold air blown on this skin when it is wet would produce a pronounced reaction. Likewise, a counterirritant would produce a reaction.  In the case of the reaction to cold the muscles under this skin area would contract.  There would be lost motion in the vertebral articulations of these metameres due to the hypertension of the muscles.  Sensitiveness to pressure and a feeling of lameness would develop.  The probabilities are that the kidneys would show marked change in function.  We have kept our reactions thus far in the metameres whose cutaneous surfaces are affected, but, clinically, we know such a condition as this is serious and hence the whole fighting power of the body is called upon to protect it from this high tension in a series of important metameres.

    Lesions Due to Functional Fatigue. - Let us reverse the picture and start with a functional disturbance of the kidneys due to too great demands on them in eliminating nitrogenous waste material.  This functional fatigue might produce muscular contraction, pain or tenderness in the spinal areas associated by innervation, i. e., the pluri-segmental areas, and thus duplicate all the phenomena mentioned in our previous description.  The field of proprio-ceptive impressions, that is the structural tissues in this particular pluri-segmental field, may likewise be the point at which all these reactions are initiated.  Injury, or functional fatigue, as is seen in street car men whose backs suffer from the constant vibration of the cars, will set up reactions which, so far as palpation is concerned, show physical signs similar to the two preceding.  After noting the physical signs, of a pluri-segmental character, it is evidently necessary to go much farther into symptomatology in order to differentiate the primary from the secondary lesion.  Since the body functions as a whole no limited pluri-segmental reactions continue without other portions of the body enter the contest for the preservation of the whole.  In the example just given the contraction of somatic muscles, tension in skin and kidney consequent on the influence of the cold air, is a condition prejudicial to the life of the body because elimination is greatly decreased and hence, unless compensatory elimination can be established, autointoxication of a fatal type will supervene.  We may conceive of an elimination center in the nervous system represented by a column of cells extending throughout the cord, controlling in all metameres the sweat function of the skin and in those metameres associated with the bowels and kidneys, the special functions of these organs.  We know all these means of elimination are coordinated and, in case of need, strongly compensatory.  The bowels must be urged to compensate for the failure of skin and kidney elimination.  Elimination may fail so quickly and completely that the consequent autointoxication and high arterial tension strain the heart.  A new group lesion representing this organ becomes apparent, and, to the physician who studies the case for the first time, at this stage offers difficulties of analysis almost insurmountable.  The spinal lesions mirror the compensatory reactions of the body.  They are guides to an understanding of the symptom complex presented in any case of disease and if studied coordinately with the symptoms often lead the mind of the physician logically to the origin of the disease reactions.