metapsychological naturally comes from the fact that we know nothing about the nature of the excitation process in the elements of the psychic systems and do not feel justified in making any assumption about it. Thus we are all the time operating with a large X, which we carry over into every new formula. That this process is accomplished with energies which differ quantitatively is an easily admissible postulate, that it also has more than one quality (e.g. in the direction of amplitude) may be regarded as probable: the new consideration we have brought in is Breuer’s proposition that we have to do with two ways in which a system may be filled with energy, so that a distinction has to be made between a ‘charging’ of the psychic systems (or its elements) that is free-flowing and striving to be discharged and one that is quiescent. Perhaps we may admit the conjecture that the binding of the energy streaming into the psychic apparatus consists in a translating of it from the free-flowing to the quiescent state. I think one may venture (tentatively) to regard the ordinary traumatic neurosis as the result of an extensive rupture of the barrier against stimuli. In this way the old naïve doctrine of ‘shock’ would come into its own again, apparently in opposition to a later and psychologically more pretentious view which ascribes aetiological significance not to the effect of the mechanical force, but to the fright and the menace to life. But these opposing views are not irreconcilable, and the psycho-analytic conception of the traumatic neurosis is far from being identical with the crudest form of the ‘shock’ theory. While the latter takes the essential nature of the shock as residing in the direct injury to the molecular structure, or even to the histological structure, of the nervous elements, we seek to understand the effect of the shock by considering the breaking through of the barrier with which the psychic organ is provided against stimuli, and from the tasks with which this is thereby faced. Fright retains its meaning for us too. What conditions it is the failure of the mechanism of apprehension to make the proper preparation, including the over-charging of the systems first receiving the stimulus. In consequence of this lower degree of charging these systems are hardly in a position to bind the oncoming masses of excitation, and the consequences of the breaking through of the protective barrier appear all the more easily. We thus find that the apprehensive preparation, together with the over-charging of the receptive systems, represents the last line of defence against stimuli. For a great number of traumata the difference between the unprepared systems and those prepared by over-charging may turn the scale as to the outcome: with a trauma beyond a certain strength such a difference may no longer be of any importance. When the dreams of patients suffering from traumatic neuroses so regularly take them back to the situation of