With regard to the war neuroses, so far as the term has any significance apart from a reference to the occasion of the appearance of the illness, I have explained elsewhere that they might very well be traumatic neuroses which have arisen the more easily on account of an ego-conflict.[14] The fact mentioned on page 9, viz. that a severe injury inflicted at the same time by the trauma lessens the chance of a neurosis arising, is no longer difficult to understand if two circumstances emphasised by psycho-analytic research are borne in mind. First that mechanical concussion must be recognised as one of the sources of sexual excitation (cp. the remarks: ‘The effects of swinging and railway travelling’ in Drei Abhandlungen zur Sexualtheorie, 4. Auflage 1920); and, secondly, that a painful and feverish illness exerts for the time it lasts a powerful influence on the distribution of the libido. Thus the mechanical force of the trauma would set free the quota of sexual excitation which, in consequence of the lacking preparation by apprehension, has a traumatic effect: but, on the other hand, the contemporaneous bodily injury would bind the surplus excitation by the putting in of a claim to a narcissistic over-charging of the injured part (see ‘Zur Einführung des Narzissmus’, Sammlung kleiner Schriften zur Neurosenlehre, IV. Folge, 1918). It is also known, though the idea has not been sufficiently made use of in the Libido theory, that disturbances in the distribution of the libido so severe as those of melancholia may be removed for a time by an intercurrent organic disease; in fact even the condition of a fully developed dementia praecox is capable of a transitory improvement in these circumstances. V The fact that the sensitive cortical layer has no protective barrier against excitations emanating from within will have one inevitable consequence: viz. that these transmissions of stimuli acquire increased economic significance and frequently give rise to economic disturbances comparable to the traumatic neuroses. The most prolific sources of such inner excitations are the so-called instincts of the organism, the representatives of all forces arising within the body and transmitted to the psychic apparatus—the most important and most obscure element in psychological research.