Thus it happens that, in spite of the numberless examples of the depressing effects of poisons discovered by pharmacologists, it is only in rare instances that the physical nature of these processes is more closely studied. Therefore, investigation in pharmacology and toxicology in so far as they are carried out in a purely scientific spirit and not influenced by the desire for merely superficial results, may find here a wide field of research work, rich in future promise. It is from such investigation that we may expect an abundance of material for the closer analysis of the processes of depression. For the present, however, we must restrict ourselves to the consideration of some individual cases which have been studied somewhat more in detail by physiologists. Simple reflection shows the possibility that depression, that is, the retardation of the normal vital processes, can be brought about in various ways. As on the one hand the normal metabolism of rest is composed of very numerous chemical constituent processes, and on the other hand the closest interdependence exists between these individual constituent processes, it follows that every factor which increases or retards even one of these must secondarily influence the course of the entire activity. Hence a wide range of possibilities exists for the processes of depression. As the complicated works of a clock can, by the stopping of a single moving part, be brought to a standstill, so in like manner the metabolic activity can be depressed by very different constituent members. In spite of this we have every reason to assume that the greater number of all processes of depression result from the primary effect of one or a few constituent members. A primary simultaneous depression of all or at least of numerous constituent processes of the entire metabolism may only be assumed as possible, resulting from decrease of temperature within certain limits. But even in the case of “_cold depression_” it is not probable, owing to the great effect of every alteration in the relations of masses in the cell, that depression is solely the manifestation of a _uniform_ retardation of all individual constituent metabolic processes. If, therefore, the greater part of the processes of depression are brought about by the primary effects of an individual constituent process, then the possibility must be admitted that _any_ component of the chain can by the means of some specific external influence form the starting point for a depression. The number of the various kinds of processes of depression would be, therefore, enormous. The knowledge obtained up to the present shows, however, that this variety is not quite as great as the above facts might lead one to expect. Even though future investigation will certainly not do away with the assumption of the existence of the most manifold physical types of depression, the analysis of a few processes which have been studied