_Contents_: Examples of effects of interference of stimuli in unicellular organisms. Interference of galvanic and thermic stimuli in Paramecia. Interference of galvanic and thermic stimuli and narcotics. Interference of galvanic and mechanical stimuli. Interference of galvanotaxis and thigmotaxis in Paramecia and hypotin infusoria. Real or homotop interference, apparent or heterotop interference. The two effects of homotop interference of excitations: Summation and inhibition of excitations. Theory of the processes of inhibition. _Hering-Gaskell_ Theory. Inhibition as an expression of the refractory period. Individual possibilities of interference of two stimuli. Interference of an excitating and a depressing stimulus. Interference of two depressing stimuli. Interference of two excitating stimuli. Analysis of the interference of two excitations. Interference of two single stimuli. Conditions upon which the result of interference is dependent. Heterobole and isobole living systems. Intensity of the two stimuli. Interval between the stimuli. Specific irritability and rapidity of reaction of the living system. Latent period. Interference of single stimuli in a series. General scheme of the development of the effect of interference. Summation and inhibition. Apparent increase of irritability. Conditions of summation. Tonic excitations. Conditions of inhibitions. Various types of inhibition. Interference of two series of stimuli. Relations in the nervous system. Peculiarities of the nerve fibers. Conversion of the nerve by relative fatigue from an isobolic into a heterobolic system. 189 IX _Contents_: Necessity of cellular physiological analysis of toxic depressions by pharmacology. Apparent variety of processes of depression. Depression of oxydative disintegration as the most extended principle in the processes of depression. Asphyxiation, fatigue, heat depression, as a consequence of restriction of oxydative disintegration. Narcosis. Theories of narcosis. The alteration of specific irritability and conductivity in narcosis. Depression of oxydative processes in narcosis. Asphyxiation of living substance when oxygen is present during narcosis. Persistence of anoxydative disintegration in narcosis. Increase of the same by stimuli. Depression by narcosis as a form of acute asphyxiation. Hypothesis on the mechanism of depression of oxygen exchange by narcotics. Possibility of combining the facts with the observations of _Meyer_ and _Overton_. 235 IRRITABILITY CHAPTER I THE HISTORY OF THE SUBJECT