Of those nerves mentioned as traceable, only such as are _irritated_ and consequently swollen and tender, can be followed. If a nerve is very heavily impinged, especially if the impingement be chronic, it is partially or wholly paralyzed and not traceable. If the heavy impingement be acute, or if there be a light impingement serving as a mechanical irritant, nerve-tracing is a real aid to diagnosis. Proportion of Cases with Traceable Nerves About one-half of all the cases which visit Chiropractors for adjustment are susceptible of nerve-tracing. In the remaining half it is absolutely impossible to acquire any information in this way. Of the half who are at all susceptible, it is possible in perhaps four-fifths of all cases to secure _some_ accurate or reliable information. The patient in whom all accessible nerves seem tender to light palpation is hyperesthetic and unavailable for tracing. 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