Now, the conception of time has been entirely revolutionized by Einstein himself; and it may be expected that the conception of causality, too--which, in accordance with custom, we still endow with a separate existence--will also be affected by this revolution. We thus approach a relativization of causality, and we may advance a step further in this direction, if we call to mind the differences of time-perception that Nature herself leaves open to us. It must be clearly understood that we are not dealing at present with the theoretical time of physics, in the sense of Einstein's theory, but with something physiological that ultimately, however, resolves itself into a relativization of time, and hence also of the causal connexions in time. To do this, we have to follow the lines of reasoning developed by the celebrated St. Petersburg academician, K. E. von Baer, and we need extend it only very little to get at the heart of causality, if we start from his address of 1860: "Which View of Living Nature is correct?" For the human brain is a part of living nature, and hence the processes of thought may also be conceived as expressions of life. The starting-point is a figment, the fictitious character of which vanishes as soon as we approach its results. The bridge of thought may be destroyed later; it suffices to carry us temporarily, as long as it lands us in safety on the other side. The rapidity of perception, of the arbitrary motions, of intellectual life seems in the case of various animals to be proportional approximately to the rapidity of their pulse-beats. Since, for example, the pulse of a rabbit beats four times as quickly as that of a bull, it will, in the same interval of time, also perceive four times as quickly, and will be able to execute four times as many acts of will, and will experience four times as much as the bull. In the same astronomical length of time the inner life and perceptual world, in the case of various animals, including Man, will take place at different specific rates, and it is on these rates that each of these living creatures bases its subjective measure of time. Only when compared with our own measure of time does an organic individual, say, a plant, appear as something permanent in size and shape, at least within a short interval. For we may look at it a hundred times and more in a minute, and yet notice no external change in it. Now, if we suppose the pulse-beat, the rate of perception, the external course of life, and the mental process of Man, very considerably accelerated or retarded, the state of affairs becomes greatly changed, and phenomena then occur, which we, fettered by our physiological structure, should have to reject as being fantastic and supernatural, although, on the supposition of a new structure they would be quite logical and necessary. If we suppose human life from childhood to old age to be compressed into a thousandth part of its