Studies in the Osteopathic Sciences Basic Principles: Volume 1 Louisa Burns, M.S., D.O., D.Sc.O. 1907  
  CHAPTER XVI.  

  EXTERNAL CHANGES AFFECT ABNORMAL RATHER THAN NORMAL TISSUES.  
              It has long been accepted as an axiom that “a bad cold always settles in the weakest place,” and that “fever always goes where there is sickness already.”  There are other sayings which have the same significance.  Not all old sayings have a basis of truth; some of them have their only foundation in some tradition of witchcraft, yet others, such as these just mentioned, have a true principle underlying them.

            Much that we are able to do for the relief of suffering would be of no value if normal tissues were affected equally with the abnormal.  As a matter of clinical experience, we do affect the abnormal tissues without subjecting the normal to any interference with their activities.  It is the function of this chapter to offer some explanation of the facts as noted.

 

Variations in Metabolism.

            In the first place, the metabolism of the cells which are being subjected to abnormal influences is more or less variable in character.  If any organism is placed under circumstances of unusual stress the series of chemical changes which make up its life history becomes very changeable in nature; the waste products of metabolism are not quite those characteristic of the same organism in health; the food stuffs taken up from its environment are not just the same as those used under normal conditions, and the whole quality of the metabolism becomes changed in the effort to adapt itself to the abnormal environment.  In case of an organ of the body which is being affected by adverse influences, not only are the facts just mentioned true, but the function of the organ in the bodily economy varies in greater or less degree from that it serves in health.  This erratic condition of the metabolism of the cells laboring under abnormal conditions renders them more subject to further disturbance from changes in the environment of the body than are the cells whose metabolism is a fairly stable result of an inheritance of some generations of practically unchanged surroundings.

 

Vascular Changes.

            Another factor in this relationship is found in the quality of the walls of the blood vessels.  These are somewhat elastic, besides being muscular, and are therefore subject to distension and relaxation as the result of changes in the blood pressure and in the action of the vaso-motor nerves.  When the walls of any given group of blood vessels are relaxed, if the general blood pressure remains high, the capillary endothelium is subjected to a considerable strain.  The formation of the nutrient lymph is thereby promoted to a certain variable degree.  If the dilatation be increased to an abnormal degree, the phenomena of inflammation ensue.  If the area affected include any of the mucus membranes of the body, the goblet cells increase in function, and, if the abnormal conditions persist, they increase in numbers also.  If the dilatation is soon relieved, no permanent ill effects of the disorder are afterward recognizable.  But if the dilatation should continue for a sufficient time, the muscles of the arterioles react to the strain, as both striated and non-striated muscles usually do, by becoming longer.  This condition of the vessel wall is comparable to the condition of the gastric musculature in dilatation of the stomach.

            These results, then, in a dilatation of the blood vessels which is more or less permanent, according to the length of time during which the dilatation persists, the pressure to which the injured vessels were subjected, and the powers of recovery of the patient.  This last factor is of no especial interest in this discussion.  Now the tissues whose vessels have been dilated in some such a manner as that just described, must perform their work with a certain amount of difficulty; it may be that no abnormal symptoms result, because the organs of the body are able to perform their functions fairly well under considerable degrees of embarrassment; but if the handicap be too great, or if other injurious factors be active, the failure or malfunction of the tissues involved is apt to become very evident.  It will be conceded that the organ whose vessels are even slightly permanently dilated is not to be considered a normal organ.  These vessels are more subject to further dilatation than are normal vessels.  Therefore, any sudden contraction of the vessels supplying another part of the body, or any sudden increase in the force of the heart’s beat, exerts an ill effect upon them rather than upon the normal vessels.  The tissues in the area of distribution of the affected vessels then suffer accordingly.

            This slight permanent dilatation of the arterioles is present in the mucus membranes in the condition ordinarily called “catarrh.”  For a bad cold to “settle” in any part of the body is for the arterioles already somewhat weakened to become greatly dilated by a sudden rise in blood pressure.  The effect of such dilatation is to induce the phenomena of inflammation, if these be not already present, or to increase them of they were already present.  Every such additional dilatation weakens the vessels and renders recovery more difficult.

 

Segmental Reactions.

            Another factor concerned in the comparative ease with which abnormal tissues are affected by external changes lies in the physiology of the nerve centers controlling the diseased organ.  The metabolism of every organ or cell group in the body is regulated by a continual stream of nerve impulses passing from the central nervous system.  Sensory impulses from any organ assist in the determination of the motor and secretory and vaso-motor impulses to that organ, and others related with it in structure or in function.  “All structures innervated from the same segment of the spinal cord are affected by sensory impulses reaching that segment,”  Any diseased or injured organ sends a continual stream of unusual sensory impulses into the central nervous system; these may be sent into consciousness as sensations of pain or discomfort, or they may simply initiate reflex changes in the size of the vessels or in the activity of the diseased organs, of the other structures innervated from the same segment of the cord or from the same sub-cerebral area, or other tissues in relation with it.
 
 

The Neuron Threshold.

            The repeated stimulation of any neuron or neuron system lowers its liminal value.  The more frequently nerve impulses reach any nerve center the more easily it is stimulated, and the quicker and the more pronounced is its response to stimulation.  The continual irritation of the nerve, centers by the sensory impulses initiated from the abnormal structure or the abnormal metabolism of any organ lowers the neuron threshold or liminal value of these centers and renders them more easily affected by any stimulation than are the same centers under normal conditions.

            It is evident, then, that if any series of impulses reach a certain segment of the cord, or any group of neurons, the structural relations being equal, the effect of this stimulation will be chiefly manifested by those neurons whose liminal value is lowest.  So, if any center has been receiving an abnormal number of sensory impulses, as is usually the case with centers in relation with diseased organs, it is very greatly affected by comparatively slight stimulation.  This effect is most apparent in those reflex actions which are of a segmental nature, or are apparently so.

 

Example of Segmental Reaction.

            If any structure innervated from a given segment of the cord be diseased, the neurons which control that segment have a lower liminal value than other neurons of the same segment.  This relation is of fundamental importance in determining the effects of certain therapeutic methods.

            For example, that segment of the cord which gives origin to the eighth thoracic nerve sends fibers from its lateral horn which carry impulses to the sympathetic neurons which influence the size of the blood vessels in the stomach and pancreas, and affect the secretions of the gastric and pancreatic glands.  This same segment of the cord also sends fibers from its anterior horn which terminate upon the striated inter-costal muscles.  This segment of the cord  coordinates the activity of other structures, not concerned in this illustration.  If the articular surfaces of the eighth dorsal vertebra be irritated in any manner, sensory impulses will be sent into the cord and cephalad, and also reflex impulses will be sent out over the efferent paths which will affect either the stomach, the pancreas, or the intercostal muscles, according to the comparative liminal value of the neurons governing these structures.  If the stomach be laboring with a mass of indigestible food, at the time of the irritation, the liminal value of the neuron system whose duty it is to coordinate the impulses concerned in gastric activity will probably be lower than the liminal value of the other neuron systems of the same segment.  The stomach will then be more quickly and more urgently affected by the abnormal irritation than the other structures.  The principle holds true for every segment of the cord and for every center in the medulla, pons and mid-brain, so far as their physiology in this respect has been investigated.

 

Effects of Fatigue.

            This principle in its application to the nerve centers hold true only so long as the neurons concerned are active.  After a certain time, which varies according to a large number of factors, the neurons whose liminal value has been abnormally lowered become fatigued.  At first, the effect of fatigue is to lower the liminal value in still greater degree, so that the stimuli almost negligible under normal conditions may at this time initiate excessive reactions.  Afterwards, progressive degrees of fatigue and exhaustion lessen the power of the neuron to respond to stimulation until it becomes almost, if not quite, inert and functionless.  During this period of decreased function on the part of the neurons innervating the diseased organs, its metabolism is affected less and less by external changes, and its own abnormality exerts less and less of an effect upon the other tissues of the body, by means of the nervous system.  After this time, no compensatory action is possible through the intermediation of the central nervous system, and, on the other hand, no injury is offered the other organs of the body by means of the central nervous system.  This loss of the nerve reactions may serve a useful purpose in many instances.  It forces a rest of the abnormal organ which may facilitate recovery; it may prevent the injury of other organs, and it may save the patient from useless suffering during the last of his days.

            Compensation for the lack of the functions of the diseased organ may be secured otherwise than by means of reflex action.  This compensation is always something of a patch work affair, though it is much better than no adaptation at all.

            Therapeutic methods owe much of their efficiency to the principle at the head of this chapter.  If it be desired to increase the efficiency of the muscles of the dilated stomach, for example, it is possible to stimulate the tissues near the eighth dorsal spine and thus to initiate nerve impulses which will affect the stomach, or the spinal or inter-costal muscles.

            Unfortunately for the development of a scientific and exact system of healing, but fortunately for the patients, this principle is a boon to the ignorant and careless practitioner, whether he be of never so rational school.  While the chances are about even as to whether he will help his patient or will injure him, he is not very apt to affect the normal tissues seriously unless he brings about some very severe structural changes.  The apparent cures that frequently follow unintelligent manipulations are to be explained upon the basis of this principle.  On the other hand, the very fact that abnormal tissues are more easily affected than normal readers the injury produced by unwise manipulations of the osteopathic centers in relation with the diseased organ decidedly disastrous, under certain circumstances.

            The fact that the abnormal rather than the normal tissues innervated from the same segment of the cord are most affected by sensory impulses reaching that segment renders it possible for the skilled physician to affect almost any diseased organ in almost any manner he chooses, so long as the nerve centers are not exhausted.  After this, he may secure the same end by indirect means, employing changes in general blood pressure, the activity of other organs, volitional impulses and other factors in securing either recovery, adaptation, or compensation.

            Note A.—A familiar instance is found in an aching tooth. Every jar or unpleasant sensation increases the pain in the tooth.  If one with toothache steps on a tack, the ache may be increased thereby.  And every one knows how much longer the aching tooth is than its fellows.