in the refractory period and produces no perceptible effect. Upon these factors depend the results of the interference of two rhythmic series of stimuli, whether a summation or inhibition of excitation takes place. Here is the key to the understanding of the great variety of interference effects. By determination of these various factors in a given case and their sequence, we can anticipate the nature of the interference which will follow. The complex actions brought about by the various factors, which we cannot at first clearly understand, can be at once interpreted as soon as we convert them into their elements. CHAPTER IX THE PROCESSES OF DEPRESSION _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_.