This much, however, is clearly revealed by a partial analysis. Human beings, in common with all life, are distinguished by the power of movement, and are sensitive to many forms of external stimulus:--heat, cold, electricity, or pressure. They pass their lives in rhythmic alternations of activity and repose; they breathe; they absorb food to supply energy and to maintain unimpaired the substance of their bodies; they excrete waste products. They share with plants and animals an intrinsic tendency to continue their growth for a certain period and up to a definite amount, while, at the close of the most pronounced period of growth, ability to transmit life absorbs the energy hitherto utilised for personal development, by which means the perpetuation of a species is secured. Research shows, also without possibility of question, that certain similar characteristics distinguish the mechanism of every type of animal life; though the machinery be in some cases of the simplest, in others highly complex. Thus have been revealed many secrets of man's physical nature; as, for instance, the knowledge that, in the earliest stages of their existence, higher forms of life recapitulate more or less imperfectly certain far-off ancestral phases of development, of which living specimens are still to be found on the lower branches of humanity's huge genealogical tree. By means also of the close and detailed observation of these lowlier organisms a clearer conception has been formed of the intricacies of growth and the prolonged process of development in mankind. Just how human beings have come to be what they are, mentally and morally as well as physically, is a still unsolved problem. There are, of course, many missing chapters in the long story of life, though so far no contradictions have been detected in its arguments. The sad side of this biological lore exists in the now ascertained fact that the highest intellectual and moral powers, those last to develop, are the first to suffer arrest or to die away when the organism is subjected to premature exhaustion or to precocious responsibility. Predisposing causes are found in disease, dissipation, or defective nurture.