It is a truism that successful treatment in any branch of medical practice, or, indeed, in a wider sense, in any activity in which we may be engaged, depends on an adequate and exact knowledge of the relation of cause and effect, and the conscientious clinician who bears that fact in mind finds the present position of clinical psychiatry one of great difficulty. As a highly esteemed physician remarked a little while ago—during one of those outbursts of professional candour which seem to be necessary at times in the interest of our self-respect, so far as our capacity to really modify the condition of our patients is concerned, we are in the position of interested observers, for we may arrange conditions, we may guard against added stresses, but do what we will, and however hard our endeavour, our patients alter, some to improve, others to deteriorate, with an aggravating indifference to our efforts. It behoves us, then, to be extremely critical of our assumptions in any particular case, to be as precise and as adequate as possible in our description of the whole train of events, and to review very carefully any deductions we may make as to the relation of possible cause and effect.