CHAPTER XLI.

Fig. 45.—TRAP AND BALL.

866.Why is the ball propelled upward, in the game of trap and ball, when the trigger is struck?

Because, when the trigger is struck at A, it is forced downwards, turning upon the fulcrum B, the opposite end, forming the spoon, is thereby forced upwards, describing a smallarc, or curved line; but directly the ball is set free from the spoon, it rises in aright linewith thedirection it was taking, at the moment it was set free.

Fig. 46.—BAT AND BALL.

867.What principles of natural philosophy are illustrated by the results of bat and ball?

Percussion, when the bat strikes the ball;rotatory motion, when the ball is sent whirling away;momentum, which it acquires by velocity;elasticity, when it rebounds from an object against whichit strikes;reflected motion, when it is turned by a body upon which it impinges;friction, as it rolls along the ground; thecommunication of force, when it sets another body in motion against which it strikes;gravitation, when it falls to the earth; andinertia, when it lies in a state of rest.

"A wise son makes a glad father: but a foolish son is the heaviness of his mother."—Proverbs x.

868.Why do pith-tumblers always pitch upon one end?

Fig. 47. PITH-TUMBLER.

Because theleadB isspecifically heavierthan thepithto which it is attached; it therefore always falls undermost; and as the lead is rounded off, just like the spill of a top, after the head has oscillated a little, and expended the force of the momentum of its fall, it will settle upon itscentre of gravity, or the point through which it isattracted to the earth.

869.Why do the figures upon the "Thaumatrope" appear to dance, when they are made to revolve before a mirror?

Because the eye, in looking through the holes in the card, towards the reflections in the mirror, receives arapid succession of impressions. As the figures upon the card are represented in a graduated series of positions—thefirstone standing upright, thesecondwith his knees a little bent, thethirda little more bent, as in the act of springing, and so on, thefigurebeing in each casethe same, but the positionslightly altered, imparts an impression to the mind, through the eye, thatone figureis passing through aseries of motions.

Thaumatrope.—From two Greek words, meaningwonderandto turn.

We have said enough, we hope, to show that even the play-hours of children may be made instructive to them; and that the simplest toys may be used to illustrate some of the grandest laws of nature. Nor may this kind of instruction be confined to children alone. Grown-up people, whether participators in the sports of youth, or simple observers of their games, may gain instruction for themselves, and be the better teachers of their children, by taking an interest in their enjoyments, and giving to their minds, through the attractiveness of pastime, a taste for observing and estimating the varied phenomena which present themselves.

Moreover, we think that parental government acquires a greater power whenit leans towards the natural desires of childhood, and wins those desires into a proper direction. Love existing between parent and child is the best tie to home, and the strongest incentive to duty. There is also something in the gentleness of childish nature which may influence for good the sterner mould of man, too often warped and clouded by the cares of life.

Jesus said, Suffer little children, and forbid them not, to come unto me; for of such is the kingdom of heaven."—Matthew xix.

Fig. 48.—THAUMATROPE, OR "WONDER-TURNER."

In Kay's "Life of Sir John Malcolm," we find an admirable and apt passage. Sir John says:—"I have been employed these last few hours with John Elliot, and other boys, in trying how long we could keep up two cricket-balls. Lord Minto caught us. He says he must send me on a commission to some very young monarch, for that I shall never have the gravity of an ambassador for a prince turned of twelve. He, however, added the well-known and admirable story of Henry IV. of France, who, when caught on all fours carrying one of his children, by the Spanish envoy, looked up and said, 'Is your excellency married?' 'I am, and have a family,' was the reply. 'Well, then,' said the monarch, 'I am satisfied, and shall take another turn round the room,' and off he galloped, with his son on his back flogging and spurring him. I have sometimes thought of breaking myself of what are termed boyish habits; but reflection has satisfied me that it would be very foolish, and that I should esteem it a blessing that I can find amusement in everything, from tossing a cricket-ball, to negotiating a treaty with the Emperor of China. Men who will give themselves entirely to business, and despise (which is the term) trifles, are very able, in their general conception of the great outlines of a plan, but they feel a want of knowledge, which is only to be gained by mixing with all classes in the world, when they come to those lesser points upon which its successful execution may depend."

"Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God."—Corinth. x.

869.Why do we eat food?

Because the atoms of which our bodies are composed arecontinually changing. Those atoms that have fulfilled the purposes of nature are removed from the system, and, therefore, new matter must be introduced to supply their place.

870.Why do we eat animal and vegetable food?

Because their substances are composed ofoxygen,hydrogen,carbon, andnitrogen—the four chemical elements of which the human system is formed. They are, therefore, capable of nourishing the body, after undergoing digestion.

871.Why do we masticate our food?

Because mastication isthe first process towards the digestion of food. Before animal or vegetable substances can nourish us, their condition must be entirely changed, theirorganicstates must be dissolved, and they must become simple matter, in a homogeneous mass, consisting of the four chemical elements necessary to nutrition, and they must again be restored to an organic condition.

872.Why does saliva enter the mouth when we are eating?

Because, in addition to themechanicalgrinding of the food by the action of the teeth, it is necessary that it should undergo certain chemical modifications to adapt it to our use. There are placed, therefore, in various parts of the body,glands, which secrete peculiar fluids, that have a chemical influence upon the food.

The first of these glands are thesalivary glands of the mouth, which pour out a clear watery fluid upon the food we eat, and which fluid has been found to possess a property which contributes to the digestion of food.

The moisture afforded by the salivary secretion is also necessary to enable us to swallow the food.

"And the Lord said unto him, Who hath made man's mouth? or who maketh the dumb, or the seeing, or the blind? have not I the Lord?"—Exodus iv.

873.Why does the salivary juice enter the mouth just at the moment that we are eating?

Because the glands, which are buried in the muscles of the mouth, and which in their form are much like bunches of currants, are always full of salivary secretion. There are nerves which are distributed from the brain to these glands, and when other nerves which belong to the senses of taste, of sight, or of feeling, are excited by the presence of food,a stimulusis imparted to the salivary glands, through the nerves that surround them, their cells collapse, and the juice which they contain is poured out through their stems, or ducts, into the mouth.

874.How do we know that impressions imparted to one set of nerves, may be imparted to another set, so as to put any particular organ in action.

Because very frequentlythe mere sightof rich fruit, or acid substances,will cause the saliva to flow freely. In this case it is evident that the salivary glandscould not see or knowthat such substances were present. An impression must, therefore, be made upon the brain,through the organ of vision, and the desire to taste the substances being awakened, a nervous stimulus isimparted to the glands of the mouth, and they at once commence their action,as if food were present.

875.Why does food descend into the stomach?

Because, after the teeth, the tongue, and the muscles of the mouth generally, have rolled the food into a soft bolus, it is conveyed to the back of the mouth, where it is set upon the opening of the throat (œsophagus). It does not then descend through the throat by its own gravity, because the throat is generally in a compressed or collapsed state, like an empty tube; and we know that persons can eat or drink when with their heads downwards. The œsophagus is formed of a number of muscular threads, or rings, andeach little thread is like a hand ready to grasp at the morsel that is coming. As soon as the bolus is presented at the top of the throat, these little muscular hands lay hold of it, and transmit it downward, passing it from one to another, until it is conveyed through the long passage, to the door of the stomach, which it enters.

"Remove far from me poverty and lies; give me neither poverty nor riches; feed me with food convenient for me."—Proverbs xxx.

Fig. 49.—SECTION OF THE STOMACH, &c.

A. The inner coat of thestomach. (The stomach is here represented cut through its length, so that we can see its inside.)

B. The lower extremity of the throat, orœsophagus, through which food enters the stomach.

C. The passage out of the stomach, called thepylorus, where a muscular contraction prevents the escape of undigested food.

D. Theduodenum, and the ducts through which thebileandpancreaticjuices enter and mingle with our food.

876.Why do we not feel the food being transmitted through the throat?

Because the nerves of the body differ in their powers: some are nerves offeeling, some ofmotion, and others are nerves of thesenses. The nerves of feeling are most abundantly distributed to those partswhere feeling is most useful and necessary to us. But the faculty of feeling our food undergoing digestion would be no service to us whatever; therefore the nerves ofmotionare plentifully distributed to the throat and stomach, but very few of the nerves offeeling—just as many as will tell us when we eat anythingtoo hot, ortoo cold, or that the stomach isout of order.

877.Why do we feel uneasy after eating to excess?

Because the stomach isdistended, and presses upon the other organs by which it is surrounded.

"Who satisfieth thy mouth with good things; so that thy youth is renewed like the eagles."—Psalm ciii.

878.Why do we feel drowsy after eating heartily?

Because, while the stomach is in action,a great proportion of the blood of the body is drawn towards it, and as the blood is withdrawn from the other parts of the body, they fall into a state of languor.

879.Why does blood flow more freely to the stomach during digestion?

Because the energy of an organ isincreased by the flow of blood, which supplies thematerialof which our organs are composed, and in which thevital essence, supporting life, resides.

880.Why does excess in eating bring on indigestion?

Because the power of the stomach to digest food isgoverned by the amount of food required by the system. It seems to be an instinct of the stomach to hold back food which is in excess, and by indications of pain and disturbance to warn its master thatexcess has been committed.

881.Why is food digested in the stomach?

Because it enters the stomach in the form of a paste, produced by the action of the mouth; and directly food enters, thegastric juice, which is formed by glands embedded in the coats of the stomach, trickles down its sides. This is a morepowerful solventthan the salivary juice—it is like the same kind of fluid, only much stronger, and it soon turns the food from a rough and crudepasteinto agreyish cream(chyme). The heat of the stomach assists the operation, and the muscular threads of the coats move the cream along, in the same manner that the muscles of the œsophagus brought down the food.

The cream is passed towards the door which leads outward from the stomach (pylorus); but if, in the midst of the cream, there are any undissolved particles of food, it closes upon them, and they return again to the stomach to be further changed.

"When thou hast eaten and art full, then thou shalt bless the Lord thy God for the good land which he hath given thee."—Deut. viii.

882.Why does indigestion bring on bilious attacks?

Because theliversecretes a fluid to assist in the digestion of food. The liver is a gland—a similar organ to the glands of the mouth—and it formsbilein the same manner that they form the salivary juice. Only the liver is amuch larger gland, and a much greater quantity of blood passes through it. The liver pours its secretion into the biliary duct (Fig. 49) to mix with the grey cream as it passes onward, and to further dissolve it. But when the stomach is excited by food which it cannot dissolve, and when the owner of the stomach, disregarding its remonstrances, will persist in over-eating, or in eating things that disagree with the system, thenthe liver and the stomach sympathise, and the muscular threads, or hands, that prevail all through the alimentary organs, instead of movingonward, move backward, andthrow some bile into the stomachto assist to dissolve and remove the excessive or improper food.

883.Why does some portion of the food we eat nourish the system, while other portions are useless?

Because most food contains some particles that are indigestible, or that, if digested, are innutritious, and not necessary for the system. Theliveris the organ by whose secretion theuseful is separated from the useless; for when the bile enters through the duct (Fig. 49) and mixes with the grey cream coming from the stomach, it remains no longer a grey cream, but turns into a mass coloured by bile, having upon its surfacelittle globules of milk, small, but very white. Those minute globules of milk (chyle) are the nutritious particles derived from the food; the other portion, coloured with bile, is the useless residue, or rather thebulk from which the nutrition has been extracted.

"God hath made of one blood all nations of men for to dwell on all the face of the earth."—Acts xvii.

884.Why does the milky, or nutritious matter, separate from the innutritious, upon admixture with bile?

Because the bile contains an oily matter whichrepelsthe waterymilk of nutrition.

Thepancreatic juicealso enters through the same duct with the bile. But its precise use is not understood. It is a fluid much like the salivary secretion of the glands of the mouth.

Fig. 50.—GREAT VESSELS OF THE CIRCULATION, AND THE DUCT WHICH CONVEYS NUTRITIVE MATTER TO THE BLOOD.

A B.Jugular veinswhich return blood from the head to the heart.

C. Thesuperior venæ cava, or trunk vein, which pours the blood returned from the upper part of the system into the heart. There is a similar large vessel which meets this one and brings back blood from the lower part of the body, and they both pour the blood into the right side of the heart.

D E. The branches of thevenous systemwhich bring back the blood from the arms.

F F. Thegreat aorta, the blood vessel which conveys arterial blood from the heart, and gives off branches that supply every part of the body.

G. Another large vein which returns the blood from the muscles of the chest, &c.

H H. Thethoracic duct, which receives the newly dissolved food from the small absorbents, that collect it from the intestines. It conveys this nutrition (called chyle) upward along the back, until it reaches where the duct turns into the junction of two veins, and pours its contents into the veins bringing blood back to the heart. The nutrition, therefore, is at this moment mixed with the venous blood, and is sent to the lungs to be oxygenised.

"But now hath God set the members in the body, every one as it pleased him."—1 Corinthians xii.

885.How is the nutrition taken away from the bilious residue?

The muscular threads (or hands, as we figuratively call them) continue to push forward the digested matter through a long tube,calledthe alimentary canal, or bowels. This canal is some thirty feet in length, and is folded in various layers across the abdomen, and tied to the edge of a sort of apron, which is gathered up and fastened to the back-bone. All along this alimentary canal those muscular hands are pushing the digested mass along. But upon the coat or surface of the canal there are millions of little vessels calledlacteals, which look out for the minute globules of milk as they pass, andabsorbthem, which means that they pick them up, and carry them away. There is an immense number of these little vessels, all busily at work picking up food for the system.

Then there is a large vessel, called thethoracic duct, which comes down and communicates with those little vessels (it is a sort of overseer, having a large number of workmen,) and collects the produce of their toil, and carries it upwards to the part where it passesfrom the organs of digestioninto thevessels of circulation.

886.What becomes of the nutrition, when it has entered the vessels of the circulation?

It is sent through a large vein intothe heart, entering that organ on the right side, from which the heart propels it into the lungs, mixed withvenous blood; and the venous, or blue blood, is sent into the lungs,taking with it the milk, the formation of which we have traced.

887.Why are the venous blood and the chyle sent to the lungs?

Because the venous blood, in its circulation through the body, has parted with itsoxygen, and taken upcarbon, and it requiresto get rid of the carbon, and take up more oxygen. The chyle, also, now combined with the blood, requiresoxygen, and having obtained it, is converted intobright red blood, and the blue blood of the veins, having got rid of its carbon, which formed the carbonic acid of the breath, has again becomebright red blood. We must therefore, in pursuing our description, cease to speak of blue, orvenous blood, and of white milk, orchyle, for the two have now combined, and, with the oxygen of the air, have formedarterial blood.

"My flesh and my heart fainteth; but God is the strength of my heart, and my portion for ever."—Psalm lxxiii.

888.What becomes of the arterial blood thus formed?

It is sent back from the lungs to the right side of the heart, from which it is sent into thegreat trunk of the aorta, and from thence it passes into smaller blood-vessels, until it finds its way toevery part of the system.

Fig. 51.—THE ORGANS OF RESPIRATION.

A. Theheart.

B B. Thelungs.

C. Theaorta, and on either side of the aorta the vessels which convey the venous blood to the lungs to beoxygenised, and the corresponding vessels which return it to the heart, after it has undergone that operation. (ForaortaseeFig. 50.)

D. Thetrachea, or large air passage, through which the air passes into the spongy texture of the lungs, when we breathe.

E E.Arteriesandveins, being the trunks of the vessels that supply the head, &c.

889.Why does the chest expand when we breathe?

Because the lungs consist ofmillions of hollow tubes, andcells, which, having been emptied by throwing offcarbonic acid gasandnitrogen, become compressed, and the atmospheric airflowing into these millions of spaces, and filling the lungs, just as water fills and swells a sponge, causes them to expand, and occupy greater room.

"All the while my breath is in me, and the spirit of God is in my nostrils. My lips shall not speak wickedness, nor my tongue utter deceit."—Job xxvii.

890.How does the blood communicate with the air in the lungs?

Through thesides of very minute vessels, of which, perhaps, afine hairgives us the best conception. But these vessels aretwisted and wound round each otherin such a curious manner, that they formmillions of cells, and by being twisted and wound, a muchgreater surface of air and bloodare brought to act upon each other, than could otherwise be accomplished.

891.Why does the blood which is thus formed, impart vitality to the parts to which it is sent?

Because the blood is itselfvitalised—is, in fact,alive, and capable of diffusing life and vitality to the organisation of which it forms a part.

This is a very wonderful fact, but no less true than wonderful, that dead matter which, but a little while ago, was being ground by the teeth, softened by the saliva, and solved by the gastric juice and bile, has now acquiredlife. Nobody can tell the precise stage or moment when it began to live. But somewhere between the stomach and the lungs, melted by the gastric juice, softened by the secretion of the pancreas, separated by the bile of the liver, macerated by the muscular fibres of the bowels, taken up by the absorbents, warmed by the heat of the body, and ærated in the lungs, it has by one, or by all of these processes combined, been changed from the dead to the living state, and now forms part of thevital fluid of the system.

892.Why do we know that the blood has become endowed with vital powers?

Because, in the course of its formation, it has not only undergone change of condition and colour; but, if examined now by the microscope, it will be found to consist of millions of minute cells, or discs,which float in a watery fluid. The paste produced by mastication consisted of a crude admixture of the atoms of food; the cream (chyme) formed from this in the stomach, presents to the microscope a heterogeneous mass of matter, exhibiting no appearance whatever of a new organic arrangement; the milk (chyle) which is formed in the intestines is found to contain a great number of very small molecules, which probably consist of some fatty matter; as the chyle progresses towards thethoracic duct(Fig. 50), it appears to contain more of these, and slight indications present themselves of the approach towards a new organic condition.

But wherevervitalisation begins, no human power can say with confidence. Yet there can be no doubt that the blood is bothorganisedandvitalised, and that it consists of corpuscles, or little cells, enclosing matters essential to life.

"But they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run and not be weary; and they shall walk and not faint."—Isaiah xl.

893.Why does the blood circulate?

Because all the bones, muscles, blood-vessels, nerves, glands, cartilages, &c., of which the body is composed, are constantly undergoing achange of substance. It is a condition of their life, health, and strength, that they shall be "renewed," and the blood is the great source of thematerialsby which the living temple is kept in repair.

894.How is the body renewed by the blood?

Every drop of blood is made up of a large number of corpuscles, each of which contains some of the elements essential to the wants of the system.

Let us, to simplify the subject, consider the blood vessels of the body to be so manycanals, on the banks of which a number of inhabitants live, and require constant sustenance. The corpuscles of the blood are theboatswhich are laden with that sustenance, and when the heart beats, it is a signal for them to start on their journey. Away they go through the arch of the greataorta, and some of the earliest branches which it sends off convey blood to the arms. We will now for a moment dismiss the wordartery, and keep up the figure of a system of canals, with a number of towns upon their banks.

"Though hand join in hand, the wicked shall not be unpunished; but the seed of the righteous shall be delivered."—Proverbs xxi.

Well, away go a fleet of boats through theaortacanal, until they reach a point which approaches Shoulder-town; some of theboats pass into theaxillarycanal and Shoulder-town is supplied; the other boats proceed along thehumeralcanal until they approach Elbow-town, when another division of the boats pass into other branch canals and supply the wants of the neighbourhood; the others have passed into theulnarcanals and theradialcanals until they have approached Wrist-town and Hand-town, which are respectively supplied; and then the two canals have formed a junction across the palm and supplied Palm-town, where they have given off branches and boats to supply the four Finger-towns, and Thumb-town.

Fig. 52.—ILLUSTRATION OF THE SYSTEM OF CANALS THAT SUPPLY THE FORE-ARM WITH BLOOD.

Between A and B thebrachial canal, which gives off branches to supply Elbow-town, &c., and then divides into two main courses, diverging to the opposite sides of the arm, and sending a smaller canal down the centre.

D D. The point where theulnar canaland theradial canal, after having passed and supplied Wrist-town, form a junction, running through Palm-town, and in their course giving off branches to supply the four Finger-towns and Thumb-town.

For further explanations of the engraving, see57.

895.How does the blood return to the lungs, after it has reached the extremities?

Theveinsconstitute a system of vessels corresponding to the arteries. We may say that the arteries formthe down canal, and the veinsthe up canal. The arteries, commencing in the great trunk of theaorta, branch off into large and then into smaller tubes, until they formcapillaryor hair-like vessels, penetrating everywhere.

"As for man his days are as grass; as a flower of the field so he flourisheth."—Psalm ciii.

The capillary extremities of the arteries, unite with the capillary extremities of the veins,and the blood passes from the one set of vessels into the other. As thearteries become smallerfrom the point where they receive the blood, so theveins grow larger; the venous capillaries, pour their contents into small vessels, and these again into larger ones, until the greatvenoustrunks are reached, and the blood is passed again into the heart as at first described. (Fig. 50.)

896.Why do we see blue marks upon our arms and hands?

Because large veins lie underneath the skin, through which the blood of the fingers and hand isconveyed back to the heart.

897.Why are the veins more perceptible than the arteries?

Because the arteries are burieddeeper in the flesh, for protection. It would bemore dangerous to life to sever by accident an artery than a vein. A person might bleed longer from a vein than from an artery, without endangering life; because the arteries supply thelife sustaining blood. The Almighty, therefore, has buried the arteries for safety.

898.Why when we prick the flesh with a needle does it bleed?

Because the capillary arteries and veins are so fine, and are so thickly distributed all over the body, that not even the point of a needle can enter the flesh without penetrating the coats of several of these small vessels.

"Let every thing that hath breath praise the Lord. Praise ye the Lord."—Psalm cl.

899.What occurs during the circulation of the blood?

Not only do the various parts to which the boats are sent take from them whatever they require, butthe boats collect all those matters for which those parts have no further use. The bones, the nerves, the muscles, &c., all renew themselves as the boats pass along; and all give something to the boats to bring back. One of the chief exchanges is that ofoxygenforcarbon, by which a gentleheatis diffused throughout the system. It is for this purpose thatfresh airis soconstantly necessary.

But other exchanges take place. The blood, in addition to oxygen and carbon, containshydrogenandnitrogen. But it contains its four elements invarious forms of combination, producing the followingmaterialsfor the use of the body: of 1,000 parts of blood,about779 arewater; 141 arered globules; 69 arealbumen; 3 arefibrin; 2 arefatty matter; 6 are varioussalts.

Albumen and fibrin are a kind of flesh imperfectly formed, and probably are chiefly used in repairing the muscles. The red corpuscles contain the oxygen which goes to combine with the superabundant carbon, and develop heat; the fatty matters probably repair the fatty tissues, and glands that are of a fatty nature; and the various salts contribute to the bones, and to the chemical properties of those secretions which are formed by the glands, &c., while the great proportion of water is employed in cleansing, softening, and cooling the whole, or the living edifice, and it is the medium through which all the nutrition of the body is distributed.

900.Why do we feel the pulse beat?

Because every time that the heart contracts it send a fresh supply of blood to the blood-vessels, and the motion thus imparted createsa general pulsation throughout the system: but it is more distinctly perceived at the pulse, because there a ratherlarge artery lies near to the surface.

"Thy hands have made me and fashioned me: give me understanding, that I may learn thy commandments."—Psalm cxix.

901.What becomes of the matter collected by the blood in the course of its circulation?

We have already explained that carbon is thrown off from the lungs in the form of carbonic acid gas. But there are many other matters to be separated from the venous blood, and its purification is assisted by the action of the liver, which is supplied with a large vein, called theportal vein, which conveys into the substance of the liver, a large proportion of the venous blood, from which that organ draws off those matters which form the bile, and other matters which are transmitted with the bile to the bowels. Theliverandthelungs, therefore, are the great purifiers of the venous blood. But there are also smaller organs that assist in the same work.

Fig. 53.—SHOWING THE DISTRIBUTION OF BLOOD THROUGH BRANCHES OF THE AORTA.

A. Theaorta.

B. Branches given off for theaortato supply one portion of the intestines.

C. Branches given off by the aorta to supply other portions of the intestines. A complete communication may be traced between these vessels from the origin of one to that of the other.

D. Thepancreas, or sweetbread, a large gland that forms the pancreatic juice, which it pours in through the duct. (SeeFig. 50.)

E E E. Thelarge intestines, forming the termination of the alimentary canal.

902.Why when we cut our flesh does it heal?

Because the blood coagulates over the cut, and throws out a kind oflymph, which forms an incipient flesh, and excludes the air while the blood-vessels are engaged inrepairing the part.

"And God said, Let us make man in our own image, after our likeness; and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing."—Gen. i.

903.Why, since all the substance of the body undergoes change, do we preserve the same features throughout our lives?

Because our substance changes in theminutest atoms; and each separate atom has a life of itself, the maintenance of which preserves theunity and permanence of the whole.

904.Why do moles upon the skin continue permanent, while bruises and wounds disappear?

Because moles are themselvesorganised formations, and repair themselves just as any other part of the body does. But bruises and wounds are the result ofaccidental disturbances, which in course of time become removed.

905.Why do the marks of deep cuts sometimes remain?

If the cut is so deep and serious as to destroy thesystem of vesselswhich supply and repair the part, then it is evident that they cannot work so perfectly as when in their sound condition. Their functions are, therefore, interfered with, and instead of having flesh uniform with the other parts of the system; there results ascar, or a woundimperfectly repaired.

906.Why when we hold our hands against a candle-light do we perceive a beautiful crimson colour?

Because the fluids and vessels of the body are in some degree transparent, and the thin textures of the sides of the fingers allows the light to pass, and shows the beautiful crimson colour of the blood.

If the web of a frog's foot be brought in the field of a good microscope, and set against a strong light, the blood may be seen in circulation, with the most wonderful effect. Each vessel, and every globule of blood, can be seen most distinctly, and the junction of the arteries and veins can be clearly traced. The little boats of nutrition may be seen chasing each other in rapid succession, and when the animal exerts itself to escape, the flow of the blood increases; and not unfrequently, under these circumstances of agitation, have we seen two or three blood discs struggling together to enter a vessel that was too small for them. Again and again they have endeavoured to find a passage, until one of them happening to slip forward, got away, followed by the others!

"Know ye that the Lord he is God: it is he that hath made us, and not we ourselves: we are his people, and the sheep of his pasture."—Psalm c.

907.Why does the flesh underneath the nails look red?

Because the transparent texture of the nails enables us to see the colour of thevascular structurethat lies underneath the skin.

Vascular.—Full of vessels. In this instance, full of capillary blood-vessels.

908.Why have we nails at our fingers' ends?

Because they givefirmness to the touch, and enable us to apply the extremities of the fingers to many useful purposes for which they would otherwise be unfitted. They enable us topress the tips of the fingers, where the highest degree of sensitiveness prevails, so as to bringthe largest amount of nervous perceptioninto the sense of touch.

909.Why do white spots occur upon the nails?

Because the vascular surface underneath is attached to the horny texture of the nail; but by knocks and other causes, the nail sometimesseparates in small patches from the membranebelow, and becomesdry and opaque.

910.Why is there a circular line of whitish colour at the root of the nail?

Because there the nail isnewly formedby the vascular substance out of which it grows, and has not yet assumed its proper horny and transparent nature.

911.Why is the eyeball white?

Because the blood-vessels that supply its surface are so very fine that they do not admit thered corpusclesof the blood.

912.Why does the eyeball sometimes become blood-shot?

Because, under exciting causes of inflammation, theblood-vessels become distended, and the red corpuscles enter, producing a net-work of red blood-vessels across the white surface of the eye.

913.Why are the lips red?

Because the lips are formed of themucous membranethat lines the body internally, and covers the surface of most of the internal parts. This membrane contains a great number of minute red vessels, which give softness and moisture to the surface. A very beautifulillustration of the softness, moisture, and delicate colour of the mucous membrane is afforded by turning up and examining the under surface of the upper eyelid.

"Hast thou not known, hast thou not heard, that the everlasting God, the Lord, the Creator of the ends of the earth, fainteth not, neither is weary? there is no searching of his understanding"—Isaiah xl.

914.Why do delicate persons look pale and languid?

Because, generally from the want of exercise and fresh air, their blood is deficient of the healthy proportion ofred corpuscles.

915.Why does exercise and fresh air impart to healthy persons a red and fresh appearance?

Because the redness of the blood is due to theamount of oxygenwhich it contains, and air and exerciseoxygenisethe blood, and diffuse it throughout the system.

916.How is the blood propelled through the arteries?

By the very powerful contraction (and alternate dilation) of the thickmuscles of the heart, assisted also by themuscular cords of the blood-vesselsthemselves, and in many instances by thecompression of the musclesin which the arteries lie embedded.

917.Why are the capillary arteries capable of receiving the great quantity of blood sent out through the larger vessels?

Because the capillary vessels areso numerous, that though they are infinitely smaller, they are capable of receiving in their minute tubesthe whole of the quantity of bloodtransmitted to them through the larger vessels.

918.Why, when we sit with our legs crossed, do we see the foot that is raised move at regular intervals?

Because the pressure upon the muscles of the leg retards the progress of the blood until it forcesitself through the compressed vessels, and thereby imparts a pulsation which moves the leg and foot.

919.Why are capillary blood-vessels found in every part of the system?

Because it isthrough these small vessels alonethat the substances of the body are renewed and changed. Even the larger blood-vesselsdo not sustain themselves upon the blood which they contain, but receive into their coats numerous capillary vessels by which they are nourished.

"All my bones shall say, Lord, who is like unto thee, which deliverest the poor from him that is too strong for him, yea, the poor and the needy from him that spoileth him?"—Psalm xxxv.

920.How much blood does the human body contain?

Fromtwenty-fivetothirty-fivepounds. (See623.)

921.How does the blood ascend in the veins, in opposition to gravitation?

In addition to the muscular coats of the veins, and the influence of muscular action upon them, there are in the veins numerous semi-circular valves, which are not found in the arteries. These valves extend from the sides of the veins in such a manner that they allow the free passage of the blood upwards, but a backward motion of the blood would expand the cup-like valves and stop the passage; so that the blood can only move in one direction, and thattowards the heart.

922.How frequently does the total amount of blood circulate through the system?

The blood circulates once through the body in abouttwo minutes. If, therefore, we estimate the amount of blood at twenty-four pounds, it follows that no less thantwelve pounds of blood pass through the heart every minute; and it is estimated that if the blood moved with equal force in a straight line it would pass throughone hundred and fifty feet in a minute.

923.How many bones are there in the human body?

There aretwo hundred and forty-six, and they are apportioned to the various parts of the body in the following numbers:—

"Our bones are scattered at the grave's mouth, as when one cutteth and cleaveth wood upon the earth."—Psalm cxli.

924.Of what substances are the bones composed?

One hundred parts of bone consist of

925.What are the uses of the bones?

Theyprotectsoft and delicate organs; they form a framework to which the organs are attached, and by which they arekept in their places; and they supply amechanism, by which themotions of the body are produced, in combination with the muscles.

926.Why is the brain placed within the skull?

Because that delicate and vital organ, being thecentre and the root of the nervous system, requires a position of thegreatest safety.

927.Why are the bones that constitute the vertebræ (back-bone) hollowed out, so as to form a continuous groove?

Because through that groove thespinal cordpasses out from the brain. Being in the centre of that column of bones, the spinal cord receives from them a similar protectionto that which the brain obtains from the skull.

928.Why is the head set upon the neck?

Because in that position it obtains thefreest motion, can turn inany direction, and is placed relatively to the other parts of the body, in that situation where it acquiresthe greatest possible advantage.

929.Why are the eyes placed in the sockets of the skull?

Because the bones of the skullafford protectionto the delicateand complicated structure of the eyes, and supply points of attachment, and grooves, by which the muscles are enabled toturn the eyes freely, and therebyextend the field of vision.

"Thus saith the Lord God unto these bones, Behold I will cause breath to enter into you, and ye shall live:"

930.Why are the bones of the skull arched?

Because in that form they acquiregreater strength, and hence the utmost degree of safety is combined with extremelightness of material.

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