It would be easy to criticise the standpoint thus adopted, though that is in no sense my purpose here. Two points alone may be raised. If, as some writers assert, the strain of war conditions is in itself sufficient to account for the development of a psychoneurosis without the introduction of any other factor, then how is one to explain the actual incidence of war neuroses? Neurotic symptoms amounting to a definite clinico-pathological condition are by no means so common as is sometimes stated. I do not know of any statistics on the matter, but I should be surprised to hear that more than 2 per cent. of the Army serving in France are affected in this way. This consideration in itself shews that some other factors than war strain must be involved, factors relating to the previous disposition of the men affected, and the problem is to determine what these are. In the second place, as to the dogmatic assertion that Freud’s theory of the psychoneuroses cannot apply to those arising under war conditions. An essential feature of this theory is that psychoneuroses result from unconscious mental conflicts. To ascertain whether these are operative in a given case, therefore, it is obviously necessary to employ some method, such as psycho-analysis, which gives access to the unconscious. It may, I think, be taken as certain that those who deny the action of these conflicts in either the war neuroses or in what, by way of contradistinction, must be called the peace neuroses, have not thought it necessary to use any such method, and they thus place themselves in a position very similar to that of a writer who would on _a priori_ grounds deny the details or even the existence of histology without ever having looked through a microscope, the only avenue to histology. I choose this simile because it seems to me that the relation of psycho-analysis to clinical psychiatry is not at all inaptly described[8] as being like that of histology to anatomy. Or one might draw an analogy from a strictly medical field. If some one were to take a series of cases of tuberculosis supervening on measles or typhoid, and then maintain that because this ætiological factor was present therefore no microorganism could be, so that Koch’s views as to the causation of tuberculosis were entirely unfounded, one would surely have the right to ask whether any search for the bacillus had been made in the cases in question, and to satisfy oneself that the observer had grasped the difference between essential and merely exciting causes of disease. If the answer to both these inquiries were in the negative, I think it will be agreed that no great weight would be attached to the claim that Koch’s theory of the nature of tuberculosis had been demolished. Yet this is precisely the order of scientific thinking evinced by those who maintain that Freud’s theory of the neuroses has been demolished by the simple observation that they may manifest themselves under the stress of warfare.