INTRODUCTION. FROM the earliest times, philosophers have considered the course of human life as divisible into three distinct periods,-growth, maturity, and decay, or childhood, manhood, and age;—and this division is, on the whole, sufficiently correct for all useful purposes. It would be difficult to fix any precise limits to each division, as it is manifest that the greatest possible variety occurs, and that descent, climate, education, and mode of life have each great influence in retarding the growth and decay of races and classes, as compared with other races and classes, or of individuals of any one race or class, as compared with other individuals of the same race or class; yet by a comparison of many individuals, general deductions might fairly be drawn for each class, or by comparing various classes and races, general conclusions for the whole human family might be fairly arrived at; and we might thus learn, 1st, what is the average dura 1 tion of life; and, 2dly, how that period is on the average divided. But as such laws would be deduced from a comparison of all classes, they could not be strictly applicable to any one. It is better to limit our inquiries, if we desire that they should be practically useful. It is, therefore, my purpose in this essay to consider the life of man as presented to our observation in the age and country in which we live, and to regard variations of climate, race, &c. only so far as they may serve to elucidate our inquiries. Passing quickly over the period of growth, 1 propose to take the human frame when fully developed and matured, when at its greatest point of perfection, and to inquire, 1st. What is the corporeal and mental condition of man when at a state of maturity, and what his physical and mental condition when age has come upon him? also to show how, when unaffected by disease or accident, he passes gradually from maturity to age, and sinks at length into the arms of death. 2d. To inquire what is the extent of longevity which such healthy individuals may hope to attain, and how they may best be made to enjoy life, even until its close. 3d. To inquire what are the diseases to which age is most usually liable, and by what means such diseases may be avoided or mitigated. PART I. ON THE DECLINE OF LIFE IN HEALTH. CHAPTER I. A SKETCH OF THE PROGRESS OF THE ORGANISATION OF MAN FROM BIRTH TO MATURITY. It is impossible to imagine anything more helpless than a newly-born infant. If left disregarded, its existence would terminate in a few hours; and many months, nay many years, must elapse before it is capable of caring for itself. It is well that nature has made maternal affection the strongest of all human impulses, and has thrown such a charm around the helplessness of infancy, as to enlist for its protection and support the warm sympathy of all, especially of females. Destined to become most complete in organisation, endowed with marvellous mental capabilities and with a plasticity of constitution, which enables him to adapt himself to all climates and to all circumstances-to command and to employ the powers of all other animals, and to bend all nature to his will; Man, at the period of birth, appears incapable of any action except receiving and digesting food. I say receiving food, for the child is for a long time unable to make any effort to procure it.' Its proper nutriment, the mother's milk or any substitute for it, must be placed in its mouth, and thus the stomach of the little being must be filled with the pabulum vitæ, independently of any effort of its own. But this being duly done, the digestive organs actively avail themselves of it. The lacteal and other absorbent vessels greedily extract therefrom the nutritious portions to build up the future Lord of the Creation, and the refuse is quickly cast forth from the body to leave space for a further supply. The organs of respiration and of circulation are equally active with those of digestion. The breathing is very rapid; the heart acts with greater frequency (perhaps with greater force, proportionally speaking,) than at any after period of life, carrying to every part of the body the vital fluid laden with the The mechanical action of suckling is instinctive. The infant grasps and sucks anything put into its mouth; and thus, when the nipple of the mother is placed there, it seizes on it, and extracts the milk. |