That there is not the least difficulty in presenting scientific observations strictly according to these principles of conditionism, and that one can perfectly well do without the causal conception in a scientific description, I have shown by a concrete example, namely, in the fifth edition of my “General Physiology.” In the whole volume the conception of cause is only mentioned in one place, where its theoretical value is criticised, elsewhere not at all, and yet I do not think that any one will miss this conception, and indeed, if their attention is not especially called to the fact, even notice the omission. These principles of an exact conditional investigation must also guide us in the analysis of the processes of stimulation. The process of stimulation is especially apt to tempt one to employ the old conception of cause, for it belongs to that group of processes which originate from an already existing system by the addition of a new factor. An electric stimulus acts on the muscle. The muscle contracts. The stimulus is considered the cause of the contraction. But what would I explain if I were to prove that the stimulation is the cause of the contraction? The history of physiology shows us that this subject has advanced long since far beyond the stage of being satisfied with such an explanation. Today the process would only then be fully investigated if we knew the entire number of its conditions and had traced the dependency of the individual partial constituents of the whole complex process upon one another. For this, however, it is essential that we study the conditions already existent in the entire system previous to the action of the stimulus. That which we describe with the word life is an exceedingly complex process. If we analyze life, it is found to be composed of an immense number of separate constituent processes, each one being conditioned by the others. These constituent processes are the vital conditions. A vital process occurs, and must occur, where and when the whole sum of vital conditions is realized. It is identical with the sum total of the vital conditions. If only one condition is absent, then life does not exist. It is then expedient to reserve the expression “life” for the _entire sum_ of the vital conditions. When we speak of the individual constituent processes as “_vital processes_” in the plural, we must bear in mind that in reality each is not in itself life. Only the whole complex “lives,” not an individual constituent of the same. Living substance is rather the _whole_ system, and not a constituent part of the same, not a piece of protoplasm, not a nucleus and not a specific protein combination in the cell.