2. As the result of the alteration in physical conceptions biology will soon cease to draw a definite line between inanimate and living systems. The normal characters of life will be recognized as appearing in steps as one passes up the series atom, molecule, colloid, protoplasm, cell, and through further stages to mammal and man. In each class of organism a central controlling process will be discovered and its laws formulated with some precision, in terms of irreversible electrochemical processes. The process which in each organism represents the co-ordinating factor and is the life of the organism considered as a unit may for instance be described in terms of a quantity which we shall call ‘f’. ‘f’ would be such that so long as ‘f’ keeps on increasing the organism is alive, while if ‘f’ stands still the organism dies. The rate of increase of ‘f’ indicates the tempo or intensity of the organism’s life. In a simple case ‘f’ might be directly related to the intake of oxygen or food, and just as respiration and assimilation are irreversible, so is the change in ‘f’. ‘f’ must go on increasing, or else cease to represent any quantity in nature; as soon as it ceases to increase the process to which it corresponds cannot be identified any longer. The most important factors which influence the life-function ‘f’ (i.e. which affect the central controlling process in any organism) will be known before about 1950, with the result that local rebellions such as cancer will not only be controllable, but easily prevented. Harmless methods for increasing the rate of change of ‘f’, i.e. for increasing the _élan vital_ of the organism, will be discovered, so that, for instance, the duration of child-birth will be reduced to a natural minimum. If child-birth sometimes takes very long nowadays, this is presumably because the woman’s body is tired, exhausted, or partially poisoned by her mode of living, and by raising her vitality at the critical moment we may expect to be able to let the process go on at its natural speed. There must be some minimum time necessary for the act, since a vast number of complex organic processes have to complete themselves in a certain order, but probably this time is considerably shorter than that during which many women in this country have to suffer. It is already known that the Mendelian _genes_ which determine heredity are related to the rates of development of special processes in the organism, and a control over the life-tempo, or rate of increase of ‘f’ in any organism or group of cells within an organism, will provide a new method of tackling the practical problem of heredity. It is possible that hereditary tendencies to specific weakness or disease will be overcome by accelerating or retarding the rate of development of the human system at some special moment between conception and maturity.