Just as the body reacts in a purposeful way to wounds or infections or an abnormal way of living, so the psychic functions react to unnatural or injurious disturbances with appropriate means of defence. One of these purposeful reactions is the dream, in which the unconscious material constellated round a given conscious position is presented to the conscious mind in symbolic form. In this unconscious material are all those associations which have remained in the unconscious because they were only weakly emphasized but which nevertheless have sufficient energy to make themselves felt during sleep. Naturally the purposeful character of the dream-content cannot be directly seen from the manifest dream-content; it requires an analysis of this manifest content to reach the actual compensatory factors of the latent dream-content. But most physical defensive reactions are of the same scarcely recognizable and, so to speak, indirect nature, and their purposeful character also has only been recognized through deep investigation and exact observation. I might recall, for instance, the meaning of fever and the processes of suppuration in an infected wound.