In the usual case one or two nerves will be found easily traceable, while the rest exhibit no tenderness on pressure. Such a case furnishes the most reliable information securable by this method and the tender nerves may be considered as lightly or acutely impinged.
Preconception of Nerves Essential
Knowledge of the anatomy of the nervous system is a part of the necessary equipment of the Chiropractor who would trace nerves and this knowledge should be so thorough as to enable the palpater to recognize each tender line found as an anatomically described nerve-path or an error on his part. The examiner must know the paths of all nerves and be able to predict from the first tender points discovered the probable course which the tenderness will follow, so as to direct his search along that probable path.
He must be able to detect unconscious deception on the part of the patient through his knowledge of the anatomical impossibility of the apparent tracing. For instance, if for any reason he may appear to have traced a nerve upward beside the spinal column from D 10 to the eye by way of the vertex, he must know that this is an illusion—because such nerves do not exist and cannot be anatomically demonstrated—or accept the well merited ridicule of any educated person who discovers his absurdity.
Because of the difficulty of determining whether the tender structure found be muscle, nerve, or viscus, and because of the natural suggestibility of both palpater and patient, nerve-tracing cannot be so reliable a guide to nerve-paths as is dissection. It should not be necessary to state this obvious truth but the calm acceptance, by many, of the weird conclusions based upon a belief in the infallibility of nerve-tracing testifies that it is necessary.
Nerve-tracing is valuable only where the nerve-path outlined as being tender corresponds to the known path of some nerve.
Suggestion
Paradoxically, knowledge of nerve-paths may lead to error. By the law of expectancy, we are prone to find what we look for and if we hold too strongly to the belief that because we have found one or two points of tenderness we must find a series of points extending along a mentally pictured nerve-path, we may search until we falsely believe that we have found this series.
Likewise the patient, having been carefully informed as to the manner of procedure and knowing what we expect to discover, may unconsciously deceive us by feeling tenderness in response to suggestion, where no real impingement exists.