It is a commonly accepted scientific truth that the continuance of life in any living thing depends upon death.  But there are two ways of expressing this truth:  one, regarding merely the outward fact, as when we say that animal or vegetable tissue is renewed through decay; the other, regarding the action and reaction proper to life itself, whereby it forever springs freshly from its source.  The latter form of expression is mystical, in the true meaning of that term.  We close our eyes to the outward appearance, in order that we may directly confront a mystery which is already past before there is any visible indication thereof.  Though the imagination engaged in this mystical apprehension borrows its symbols or analogues from observation and experience, yet these symbols are spiritually regarded by looking at life on its living side, and abstracted as far as possible from outward embodiment.  We especially affect physiological analogues because, being derived from our experience, we may the more readily have the inward regard of them; and by passing from one physiological analogue to another, and from all these to those furnished by the processes of nature outside of our bodies, we come to an apprehension of the action and reaction proper to life itself as an idea independent of all its physical representations.

Thus we trace the rhythmic beating of the pulse to the systole and diastole of the heart, and we note a similar alternation in the contraction and relaxation of all our muscles.  Breathing is alternately inspiration and expiration.  Sensation itself is by beats, and falls into rhythm.  There is no uninterrupted strain of either action or sensibility; a current or a contact is renewed, having been broken.  In psychical operation there is the same alternate lapse and resurgence.  Memory rises from the grave of oblivion.  No holding can be maintained save through alternate release.  Pulsation establishes circulation, and vital motions proceed through cycles, each one of which, however minute, has its tropic of Cancer and of Capricorn.  Then there are the larger physiological cycles, like that wherein sleep is the alternation of waking.  Passing from the field of our direct experience to that of observation, we note similar alternations, as of day and night, summer and winter, flood and ebb tide; and science discloses them at every turn, especially in its recent consideration of the subtle forces of Nature, leading us back of all visible motions to the pulsations of the ether....

In considering the action and reaction proper to life itself, we here dismiss from view all measured cycles, whose beginning and end are appreciably separate; our regard is confined to living moments, so fleet that their beginning and ending meet as in one point, which is seen to be at once the point of departure and of return.  Thus we may speak of a man’s life as included between his birth and his death, and with reference to this physiological term, think of