_Contents_: Indicators for the investigation of the process of excitation. Latent period. The question of the existence of assimilatory excitations. Dissimilatory excitations. Excitations of the partial components of functional metabolism. Production of energy in the chemical splitting up processes. Oxydative and anoxydative disintegration. Theory of oxydative disintegration. Dependence of irritability on oxygen. Experiments on unicellular organisms, nerve centers and nerve fibers. Restitution after disintegration by metabolic self-regulation. Organic reserve supplies of the cell. The question of a reserve supply of oxygen of the cell. Metabolic self-regulation as a form of the law of mass effect, and metabolic equilibrium as a condition of chemical equilibrium. Functional hypertrophy. 87 VI _Contents_: Only processes of excitation are conducted, not processes of depression. Conduction of excitation in its two extreme instances. Conduction in undifferentiated pseudopod protoplasm of rhizopoda. Conduction of excitation with decrement of intensity and rapidity. Conduction of excitation in the nerve. Rapidity of conduction. Conduction of excitation without decrement. Relation between irritability and conductivity. Conduction of excitation with decrement of the nerve after artificial depression of irritability by narcosis. Theory of the decrementless conduction of the normal nerve. Proof of the validity of the “all or none law” in the medullated nerve. Theory of the process of the conductivity of excitation. Theory of core model (Kernleiter). Electrochemical theory of conduction based on the properties of semi-permeable surfaces. 118 VII _Contents_: Conception of specific irritability. Alteration of specific irritability during and after excitation. Refractory period in various forms of living substance. Absolute and relative refractory period. Curve of irritability during refractory period. Dependence of the duration of the refractory period on the rapidity of the course of the metabolic processes in the living substance. Dependence on temperature. Dependence on supply of oxygen. Theory of refractory period. Refractory period as basis of fatigue. Fatigue as a form of asphyxiation. Alterations of irritability and the course of excitation in fatigue. Recovery from fatigue. The rôle played by oxygen in recovery. Fatigue as an expression of the prolongation of the refractory period conditioned by the relative want of oxygen. Fatigue of the nerve. 154 VIII