How often during these recent decades when events have seemed to move faster, when discoveries and inventions have been announced at such frequent and brief intervals that we fail to note them all for lack of time, when haste and rush characterize habits alike of life and thought, do we find that we simply must stop, as it were for breath, while we unload a large amount of accumulated mental rubbish and clear a space in our storage capacity for up-to-date knowledge! It is a decennial mental house-cleaning process. We must unlearn so much of that which ten to forty years ago we so laboriously learned. We must adopt new and improved reasoning processes. But it is hard to do all this. For instance, as a boy I learned the old chemistry quite thoroughly. During a subsequent interval, when I did not need to study it, came the new chemistry, and when I again required it I had not only to study a practically new science--which was not so bad--but to rid my brain of much that had really found firm lodgment there, and this was difficult or impossible. So it is with one who, having been brought up on Euclidean geometry, finds himself confronted with the comparatively new non-Euclidean, and who has then not merely to forget, but to unlearn all those fundamental axioms which seemed so plain and so indisputable, that is, if he would accept the teachings of Bolyai and others. For example, that a straight line is not necessarily the shortest route between two points shocks our Euclidean orthodoxy, and is at the same time, _to us_, inconceivable; as also that parallel lines indefinitely prolonged _may_ touch, and the like; likewise the concept of four-dimensional spaces, or worse yet, _n_-dimensional. And now, in somewhat like manner and to a certain degree, must we revise our previous conceptions of death, at least to this extent: Not that we yet know much better than we did what it really is, but that we know more about what it is not. Even save, perhaps, in its instantaneous happening it is _but a step_ toward dissolution, usually not the first, certainly not the last, but yet the most conspicuous. Death is in many respects a biochemical fact. It is so intertwined with ionic changes in the arrangement of matter that we may hope for more information regarding some of its aspects as knowledge of the latter accumulates.