Rejuvenation will soon be safe and efficient, but not as a means for attempting immortality. It will be socially recognized as healthy and legitimate only when undertaken to compensate for premature ageing due to specific repressions, illness, or anxiety. The elimination of known diseases by a genuine science of life does not mean that other diseases will spring up perhaps worse than before. A theoretical science of life will know the meaning of all disease, and will not prevent one in such a way as to give rise to another. Instead of making campaigns against influenza or any other one disease, it will determine the conditions in which no disease can survive, and thus gradually eliminate all the organic diseases which attack the body. But this does not mean the attainment of a hygienic Utopia in which human life necessarily fulfils itself. A balance will be made to the disappearance of cancer and syphilis, not by the arising of other diseases but as a result of the consequent increase in the sensitiveness of the human brain. The supremely difficult task of the next hundred years will be to keep the mind of the race healthy and stable through a period of critical sensitiveness. We are in a transition stage of violent instability, of intense cruelty coupled with compassion (America), of blended love of liberty and need of discipline, of emotional religions and of wars--but we must hope that it will lead to some mode of life with greater inherent stability. 3. Psychology is now occupied with the discovery that the human response to perceptions is not additive, i.e. that the effect made by a group of sounds or colours depends on the pattern in space and time in which they are arranged. (_Gestalt-theorie._) For instance, the effect made on a man by the individual notes of ‘God save the King’ when played in the wrong order is negligible, and bears no relation to his response when he hears the tune played in a cinema, and it reminds him of ‘patriotism’ and the War. So far no scientific method has been found of describing when a group of elements is to be treated as a ‘whole’ for the purposes of psychology, and this is where the greatest advances may be expected.