The symptoms of the second group, that of functional nervous affections (neuroses and psychoses), are characterized by generality and indefiniteness of distribution, by relative variability, by easy removal or spontaneous disappearance, and by the preponderance of subjective symptoms. The affection may endure for many years or for a lifetime without fatal result and without special aggravation. The Ego is very strongly and deeply affected, fear, depression, and constant dwelling upon the symptoms being prominent features. These are general statements intended to serve as guides for the preliminary study of a case. It must be remembered that they are all liable to exceptions, and that each patient must be separately considered. It should be borne in mind that what to-day appears as a functional affection, chiefly indicated by subjective symptoms, may in a few months present distinct signs of organic changes in the nervous system. Also, it must be added that in the present state of knowledge we sometimes are not sure as to the presence or absence of organic changes even after careful study of a case; as, for example, in some epilepsies and neuralgias. Furthermore, allowance must be made for the following sources of error: Anatomical variability; as, for example, in the distribution of peripheral nerves and in the amount of decussation of fibres of the pyramids; The coincidence of diseases and multiplicity of lesions; The toxic effects of drugs taken by the patient previous to our examination; as, for example, bromism. I. The Diagnosis of Organic Diseases of the Nervous System. This should invariably consist, in the observer's mind at least, of three separate diagnoses, each formed by the application of widely different sources of knowledge, and each requiring a different logical process. One diagnosis forms the indispensable preliminary to the others, and the last one, when correct, demonstrates that the neurologist is a physician as well as a specialist. A further utility of this procedure by the method of the threefold diagnosis is, in our opinion, that it constitutes the sure inductive reasoning to be employed in the search after the pathology of new diseases, and must prove of help in the future growth of neurological medicine. These diagnoses are— The diagnosis of the symptoms or symptom-group; The diagnosis of the location of the lesion; The diagnosis of the nature of the lesion or of the functional disorder.