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. Place in Diagnosis The value of nerve-tracing in diagnosis has been much overestimated by many, though the tendency of the profession seems to be toward rationalism along that line. Whereas, in palpation of the spine every real subluxation gives evidence of disease, or tendency to disease, while every normally aligned pair of vertebrae furnish proof that no disease can exist in the area of distribution of the nerve emerging between them, nerve-tracing is much less reliable. If the tender nerve be traceable to a vertebral subluxation it may be taken as additional evidence that the effect of that subluxation is _disease_, rather than _tendency_ to disease, truly an important distinction, but scarcely broad enough to support a diagnosis without aid. The absence of tenderness from nerves does not negative a disease in any instance, whereas the absence of subluxation _does_. Like all other expedients for the selection of vertebrae for adjustment without admitting the necessity for first acquiring much skill by much labor, nerve-tracing has a great weakness. Only irritated nerves are tender and the effects of subluxation may be either irritation or paralysis. If accurately done, sources of error carefully eliminated, and the results of nerve-tracing found to correspond with the condition of the spine and the other symptoms, this method of demonstrating to the patient the connection between the vertebrae and the diseased region of his body is valuable. It aids in convincing him of the validity of the Chiropractic theory. TECHNIC OF NERVE TRACING Where to Begin The palpater, having made his vertebral palpation, may begin at some point in the body indicated by the symptoms as diseased and, finding tenderness, follow the path of a nerve back to the spinal column where the nerve may be fairly presumed to enter the intervertebral foramen. Or he may use his palpation record as a guide and follow the tender nerves outward to their periphery. This is the better method. [Illustration: Fig. 5. Technic of nerve tracing, showing position of fingers and marking of tender points.] Palpation as Guide