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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

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Cho of life; and, 2dly, how that period is on the smage divided. But as such laws would be deduced tfnxn 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.

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PART I.
ON THE DECLINE OP LIFE IN HEALTH.

CHAPTER I.

A SKETCH OF THE PROGRESS OE THE ORGANISATION OE MAN EROM BIBTH 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 vita, 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.

matters requisite for its development and growth. Thus, then, from the very commencement of existence, the processes of organic life are fully performed. The ingestion and digestion of food, the extraction of its nutrient portions, their distribution and deposition throughout the body, and the removal therefrom of whatever is useless or effete.

But the powers of animal life appear as yet scarcely to exist. The little creature is unable to support itself; the movements of the limbs are involuntary and without design; nor is there the slightest manifestation of the existence of mind, the infantile cry being only an indication of pain or of hunger. Only by slow degrees do the various organs of the body assume their due consistency, the functions of animal life gradually appear, and the existence of the mental powers become evident. All the processes of early life seem to have but one object,—the perfection of the various organs, that is their complete development and growth up to the most mature condition. To understand this, let us take a slight review of the condition of the various organs of an infant. The food of the infant has been already prepared in the system of the parent, and does not require to be masticated. The absence of the teeth is therefore unimportant, and the fluidity of the nourishment is best

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