_Psychomotor retardation_ is an underactivity of both mind and body in which consciousness is dulled and the body sluggish. A _neurosis_ is a disorder of the nerves, which may be functional or organic. _Nervousness_ is properly termed a _psychoneurosis_--for we have learned that there can be no neurosis without an accompanying psychosis. _Psychosis_ is the technical synonym for insanity. _Borderland_ disorders constitute a group in which mental perversions do not yet so dominate reactions as to make them irrational. Twilight is neither night nor day; the feelings of the hysteric are not insane, but the actions may be. _Insanity_ is a prolonged departure from the individual's normal standard of thinking, feeling, and acting. _Mania_ is insane excitement. _Melancholia_ is the inability of the mind to react to any stimulus with other than gloom and depression. Melancholia may be of the intellectual type or of the emotional type. The patient who tells you constantly that he has murdered all his children, that he is a criminal beyond the power of God to redeem, who seems chained to his delusions, yet shows no adequate feeling reaction, no genuine sorrow, we call a case of the intellectual type of melancholia. Another patient misinterprets every normal reason for happiness until it becomes a cause of settled foreboding. The mother, whose son fought safely through the war and is now returning to her, feels that his coming forecasts calamity for him. He had better have died in France. She is of the emotional type of melancholia. _Hysteria_ is a nervous disorder based upon suggestibility, and capable of imitating most known diseases. _Insane impulses_ are morbid demands for reckless action beyond the control of the will. Example: The impulse to kill, quite regardless of who may be the victim. _Psychopathic personality_ is a term much used today to designate an hereditary tendency on the part of the individual to mental disorder. The _neuropath_ is the individual with an inborn tendency to the neurosis. _Neurotic_ is a term broadly employed for the nervous in whom emotions predominate over reason. _Neurasthenia_ is a nervous disorder characterized by undue fatiguability. _Psychasthenia_ is a nervous disorder characterized by a sense of unreality, weakness of will, self-accusation, and usually by phobias and obsessions, all subject to temporary correction by reason or influence from without. _Hypochondriasis_ is a disorder characterized by morbid attention to bodily sensations, and insistent ideas of bodily disorder. _Phobia_ is a morbid fear or dread. FACTORS CAUSING VARIATIONS FROM NORMAL MENTAL PROCESSES HEREDITY