He must make a correct diagnosis which serves to determine the nature and location of the disease process. In this he may be greatly aided by vertebral palpation and nerve-tracing, especially in differential diagnosis. Any case which affords less than a quite positively correct diagnosis should be excluded from the test list because any conclusion based on a doubtful diagnosis must itself be doubtful and may be seriously misleading. He must then ascertain as far as possible the known anatomical nerve connection between the spine and the diseased part. If several connections are known he must decide according to nervous physiology, by recognizing the morbid functions which constitute the disease and learning which nerves control these functions and which must therefore be deranged in order that the disease may exist. I may say right here that to attempt to answer the problems of Chiropractic on the assumption that standard anatomies are incorrect in their statement of nerve connections is as hopeless as the wail of the schoolboy that the answers in his arithmetic are wrong because his sums fail to come out that way. The investigator must next be accurate in Palpation, selecting the subluxation which would, from his knowledge of the body segmentation, seem most likely to influence the nerves involved, and positively ascertaining the _number_ of the subluxated vertebra. No one who cannot count vertebrae accurately can positively say which vertebra he has adjusted. More than that, no one who _has not_ counted the vertebrae in the special case in question can say which vertebra he has adjusted. No mere regional localization will suffice for scientific investigation. Correct and accurate adjustment must follow selection of the single vertebra and the adjuster must know that he has used the one special movement, or form of adjustment, which is mechanically right for that kind of subluxation and has so moved the vertebra as to release impingement. Mere movement of a vertebra is not necessarily an adjustment or even a maladjustment; it may be movement without permanent change of relation or release of impingement. (See “Preferable Adjustments,” p. 155.) There follows the observation of the progress of the case and this must be so careful and accurate that the observer knows to a certainty whether the disease is progressing unfavorably, or favorably, or whether it has been entirely eradicated. He must know the value of every changing symptom, the real meaning of each new development. Every diagnostic method should be at his command for this work. Constant vigilance and constant thought should mark each step of his work. Finally he must be so cautious and careful in his statements that no doubtful conclusion is allowed to escape from his own mind. We may believe or suspect or hope for proof of our theories but we have no right to state as a fact anything except that which has been proven under the most rigidly guarded scientific test conditions.