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They gradually unite into larger tubes, which, after passing through a series of glands, pour their contents into a common pipe or duct, about the size of a quill. This duct runs nearly parallel with the gullet. The chyle accordingly returns in a direction opposite to that pursued by the food before digestion, until it is poured into one of the veins of the neck, where it mingles with and replenishes the blood.
The purpose of digestion, then, is to make blood, and by the blood the waste of the body is repaired. Both mind and body must suffer if this important process is ill performed. The food should be wholesome and sufficient in quantity, but over-eating merely burdens the stomach, and retards its action. Above all, exercise is essential to a continuance of healthy digestion. It causes waste, and waste invites as well as gives room for repair. Besides this, exercise stimulates the organs in various ways, and is altogether one of the surest means of securing and maintaining that healthy condition of the body, which is so closely connected with a cheerful and contented mind. Viewed in this light, labour is not a curse; when it is not of a hurtful kind, nor too severe, it is blessed as well as honourable.
CIRCULATION OF THE BLOOD. The blood is a mighty river of life. As long as life itself lasts it is impetuously rushing through every part of our bodies, by means of an elaborate network of canals. It issues from the heart, bright and red, through one great artery, named the aorta, which branches and branches like the boughs of a tree, the vessels becoming smaller and smaller as they divide, till at last they are invisible to the naked eye. They are then no longer called arteries, bat capillaries. Through the walls of these microscopic tubes, with which the whole body is crowded, the blood may be said to hold communication with the tissues composing the various organs. The tissues are gradually wasting away, consumed by the vital action of the organs which they form. But the blood comes to their aid, and out of some forty substances which it carries about in its ceaseless flow, each tissue has the power of appropriating and converting into a part of itself whatever is necessary for its repair. This is the process of assimilation.
But the blood does more. It not only supplies the new material, but carries away the old. It not only brings fuel to feed the flame of life, but removes the ashes which that flame has left. Having thus exchanged its glowing red for a much darker hue, it now leaves the capillaries, and enters the veins. In general form, these are similar to the arteries; only the blood flows through them in an opposite direction. It is gathered up first by the smallest branches, along which it flows till they gradually unite, and pour the whole by a single stream into one of the cavities of the heart.
But this blood has no longer any life-giving power, and before it be sent out again to the tissues, some means must be found to purify it. Its impurities have mostly assumed the form of carbonic acid, which must be exchanged for oxygen before it can become again the supporter of life. The air is an inexhaustible reservoir of oxygen, which forms, indeed, about a fifth of the whole atmosphere; but how is that oxygen to be brought into contact with the polluted blood ? To accomplish this is the object of the lungs, it is for this that we are made to breathe. The heart again expels the blood, but this time by a different channel. The arteries which now convey it spread themselves over the lungs, exactly as those formerly mentioned did over the body. Meanwhile another process is going on. By a muscular effort the chest is dilated, and the air rushes in through the mouth or nostrils, and thence along the wind-pipe, to fill up the vacuum. The wind-pipe sends out branches over the lungs, like those of the arteries, and these terminate in minute air-vessels, which are interspersed among the capillaries containing the blood. Through the
delicate sides of their respective vessels, the blood rcccives a supply of oxygen from the air, and the air in its turn carries off the carbonic acid and other deleterious substances from the blood. The result is that the blood resumes its bright colour and life-giving energy, and returns to the heart to recommence its journey over the body.
At every breathing, a portion of the air in the lungs, laden with carbonic acid, is expelled by a contraction of the chest. Another supply is then drawn in as before, and so on, the same processes being repeated. But if the air inhaled is itself impure, the whole contents of the lungs must soon become vitiated, and the blood will return to the heart unpurified. Hence the necessity for a constant supply of pure air. None of the conditions of health is so sadly neglected as this is. Pigsties and dunghills are kept close to crowded dwelling-houses; streets are allowed to remain covered with dust and filth; houses are too often damp, illventilated, and unswept; schools and churches are kept as close as if it were wrong to admit the pure air of heaven, or allow the carbonic acid breathed from hundreds of lungs to escape. No mistake could be more dangerous, none is more fatal. Of the importance of the air we breathe some idea may be formed from the wonderful fact, that in the course of a single year, an ordinary man draws in and expels 100,000 cubic feet, by means of something like 9,000,000 of separate muscular efforts, to aërate and purify some 3500 tons of blood !
The heart is the centre of the organs of circulation, the engine that sets the current in motion. It is a muscular body, consisting of four chambers or cavities, each of which has the power of contracting so as to empty itself of its liquid contents. The two principal cavities are called ventricles; their office is to despatch the blood through the arteries. Into the ventricles it is poured by the auricles, each of which is a sort of ante-chamber to its corresponding ventricle, intended to receive the blood from the veins. Hence the action of the heart is somewhat complicated. The blood, on returning from the lungs, passes into the
left auricle, whence it flows into the left ventricle. By the contraction of the latter it is forced through the aorta to all parts of the body. Again collected by the veins, it is received by the right auricle, which discharges it into the right ventricle. Thence it is sent out to the lungs, and, after being purified, returns again to the left auricle, to pursue, without ceasing, the same unvarying course. It is kept in its proper path by a series of valves, which open freely in one direction, but effectually prevent any return current in the other. And this process is repeated, while life continues, from 70 to 80 times in a minute. At a few points in its course, as in the wrist, the arterial current may be felt; and the beating of the heart may not only be felt, but also occasionally heard. If, however, we could for a few moments see with the bodily eye into the human frame, as with the microscope we see into the transparent frames of some of the simpler animals, a scene would be unveiled which would transcend our utmost imaginings, and which we cannot contemplate, even in thought, without a thrill. It is truly well for us that we “live, and move, and have our being,” in One who is wiser and mightier than we.
QUESTIONS FOR EXAMINATION.
What causes waste in the body, and how is it repaired? What is meant by assimilation? Where does digestion commence? What process does the food undergo in the mouth? How is it conveyed to the stomach? Describe the stomach and its action. Whence comes the gastric juice? 'the bile ? the pancreatic juice? In what form does the food leave the stomach? In what form is it absorbed ? and how? How is it conveyed to the blood? What is the use of the blood ? What vessels convey it from the heart? Describe them. Where does it come into contact with the tissues ? with the air? What is the use of respiration? Why is pure air necessary? What vessels convey the blood back to the heart? Describe the heart itself, and its action. How often does it beat? Is the circulation of the blood perceptible by the senses, and how ?
THE HOPE OF HEAVEN.
WHAT is earthly rest or relaxation, whátl that release from tòill after which we so often sígh, but the faint shadow of the saints' everlàsting rest—the repose of eternal pùritythe calm of a spírit' in which, not the tension of labour only, but the strain of the moral strife with sìn, has ceased—the rest of the soul in Gòd! What visions of earthly bliss' can éver—if our Christian faith be not a fórm--compare with “the glóryl soon to be revealed?” What joy of earthly reunion' with the ràpture of that hóurl when the heavens shall yield our absent Lord to our embráce, to be párted from us! no more for ever? And if all thísl be not a dream and a fancy, but most sober truth, whàt is there to except this joyful hópe from that làwl to which, in all other deep joys, our minds are subject? Why máy we not in this case, too, think often, amidst our worldly work, of the home to which we are going, of the true and loving heart that béats for us, and of the sweet and joyous welcomel that awaits us there? And even when we máke them not, of set pùrpose, the subject of our thoughts, is there not enough of grandeur in the objects of a believer's hópel to pervade his spirit at all times' with a calm and reverential jóy?
Do not think all thís' strànge, fanàtical, impossible. If it dó seem so, it can ònly bel because your heart is in the earthly hopes, but not in the hígher and hòlier hopes-because love to Christ' is still to you but a name— because you can give more ardour of thought to the anticipation of a coming holiday, than to the hope of heaven and glory everlàsting. Nò, my friends! the strânge thing is, not that amidst the world's work! we should be able to think of our Home, but that we should ever be able to forget it, and the stránger, sádder still, that while the little day of life is pássing—mòrning, nòontide, évening-each stage more rapid than the làst, while to many' the shadows are already fast lengthening, and the declining sun wárns them' that “the night is at hànd, wherein no man can work," there should