Summary.1. The termrestitutionis suggested for the repetition of irreversible processes. I have tried to show the biological meaning of this in secretion, regeneration and growth.2. A definition is given of the termsevasion, accumulation, secretion, as three ways of elimination of material from the inside to the outside of protoplasm.3. Reception of material, formation of pre‐secretion, formation and migration of granules are outlined as different processes of restitution during secretion.4. The origin of “basal granules” in topographical connection with mitochondria in the pancreas and the influence of X‐rays on this origin is described; likewise the role of the nucleus and the ergastoplasm in other glands.5. The building up of clear‐cut granules occurs in connection with colloids of the Golgi field.6. During these processes some signs of metabolism in the cell are observed.7. Certain physiological unities responsible for restitution are calledfields of restitution.8. The size of these “fields” may be the size of microscopical particles, of cells, or of organs. Some examples of this are given.9. An outline is given of what may be the qualitative differences between the various kinds of “fields.”10. The question is answered as to how often a field of restitution is able to work. Polyphasic and monophasic systems are distinguished. The polyphasic and monophasic working of the different fields is explained in this connection.11. The secretion quotient is in function of time. If this quotient is 1, the working of a field is arhythmical. If the quotient is smaller than 1, the working must be rhythmical. The value of this quotient is given for certain cellular and organ fields.12. Various examples for synchronous and asynchronous action of cells are given.13. Two different causes for synchronous working of secretory cells are demonstrated: an abbreviation of the cycle of processes, and rhythmical mitosis.14. The relation of the “theory of fields of restitution” to growth, regeneration and the theory of “Teilkörper” (Heidenhain) is outlined.15. The influence of X‐rays on different stages of restitution is described and compared with regeneration and growth.16. The question of autonomic and heteronomic factors in the different fields