Our bodies : an elementary text-book of human physiology with 100 questions for examination

Introduction

The subject of Human Physiology is one of such interest and importance that it is not thought necessary to usher this little book into existence by an apology.

It is intended, first, to help school-teachers, by enabling them to place in the hands of their pupils a work from which they can prepare home lessons, and thus be better able to follow the lectures which may be given in the school j and secondly, to form an elementary text-book for those who are reading for examination in this subject.

The lessons are digests of the lectures I have given in the City of London Middle Class Schools, where I have found them sufficiently successful to justify me in recommending them to others.

My practice is to cause all the pupils to take notes, which they subsequently write out fairly, adding drawings of my blackboard illustrations.

I have been in the habit, before introducing the subject of the day, of calling on some boy in the class to read aloud his notes of the last lecture, by which much interest and emulation is excited.

In the illustrations I have avoided whole figures, iv

INTRODUCTION.

but all tlie parts are so arrauged that the relative position of each is obvious.

In the text no oj^portunity is lost of teaching the subject with regard to health, and thus digestion, exercise, fresh air and ventilation, cleanliness, <fcc., are especially dwelt on.

A chapter on the Microscope is apjoended, with, the view of encouraging the pupils to examine any objects of natural history which they may obtain, and to make their own observations thereon.

For much valuable assistance and instruction I am indebted to Dr. Marshall’s and Messrs. Johnston’s excellent diagrams, and to the works of Professor Owen, Dr. Carpenter, Dr. Shea, and M. Milne- Edwards.

This little book then is presented to teachers and pupils ; it treats not of man’s works, but of God’s, and thus the subject must ever command an attention higher than those which merely appeal to the intellect ; and as the being here treated of is the only one we know of in all animal creation who can elevate his thoughts to heaven, let me hope that in showing “ how fearfully and how wonderfully we are made ” I may sow some seeds which may fructify in the new soil in which it is sown, and bear fruits of gratitude to the merciful Creator of all.

ELLIS A. DAYIDSON.

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In a former little book* I have spoken to you of the way in which a house is put together, and of some of the materials employed in it.

I now intend to give you a few lessons concerning a structure more wonderful than any that man can build — the house which God has created to be the dwelling-place of the soul during its life on earth ; and I am sure that when you know how wonderfully we are made, you will be led to think of the Great First Cause, the Mighty Creator of all, and that you will try to render yourself worthy to dwell in the beautiful mansion which He has provided for you.

The Skeleton.

The human body is supported on a framework called the skeleton, which is made up of about 198 bones.

Bone is a hard and strong substance formed j)rincipally of carbonate of lime, phosphate of lime, and gelatine.

* “ Our Houses,’’ publisliid By Cassell, Pctter, and Galpiu, price IS,

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The lime is called the Mineral portion — Minerals you will remember are substances dug out of the earth, forming rocks ; and carbonate of lime we are very familiar with, as it is only limestone and chalk.

Phosphate of lime comes from rocks in which a great many remains of animals exist.

But j^ou will perhaps ask how does tlie lime get into our bones ? Well, it is contained in many articles of our food, and also in water, in this way it mixes with the blood, and the blood carries it into the bones, in a manner which I will explain to you presently.

The gelatine in bones is called the Animal portion, and is the substance which forms the jelly and glue.

Of course you know that bones are of very many different shapes, but still they may be classed into three sorts: —

The Plat, such as the Shoulder-blade ;

The Short, such as those in the Wrist ;

The Long, such as those in the Legs.

All these different bones are so arranged that each one performs exactly the duties required of it. They are nourished or fed (that is, the new particles which are to assist their growth are brought to them) by the blood in a most wonderful manner.

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To explain this, let ns take a sketch (Fig. 4) of a portion of a thigh hone, highly magnihecl, here you will see that the whole of the top is covered with small rings and openings. These openings are the months of tubes which come from the outside of the bones. Now around each bone is wrapped a strong membrane or skin, called the

Pe-ri-os-te-um, the name of which is derived fiom two Greek words, '‘Pm, about, and Osteon, a bone.” In this membrane there are a great number of blood-vessels, which becoming very small and hair-like, enter the small openings in the bones and travel through the tubes I have described. • .

(Fig. 5). Around each of the small tubes arp arranged the layers forming the bone, and between

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these layers are small open spaces, marked in black in this drawing, called Lacunse. These are joined t® each other, and to the canal which they surround by other and still smaller openings, called “ Can-alic-u-li,” and thus the nourishing Iluid passes from the blood-vessels into the very substance of the bones.

The tubes through which the blood-vessels travel are called the “ Haversian Canals,” having been discovered by Havers, a very learned doctor, who lived in London about the year 1690.

You can for a very trifling sum buy small pieces of bone, cut lengthwise and across, ground down until they are so thin that you can see through them, and mounted between two pieces of clear glass. '

You will thus be able by means of a microscope to study the structure I have described. I am anxious that you should learn to examine and think for yourself, and will, therefore, before closing this book, give you some information about Microscopes and the way to use them.

You can very easily separate the mineral and animal portions of a bone, so as to examine the manner in which each is placed.

Take a little block of bone and place it on a

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piece of tin, rake out some of the fire between the grate and the first bar, so as to form a sort of oven, and put your bone on its little tray in this. The heat will gradually burn away all the gelatine, leaving only the earthy portion. You must then with the tongs draw out your tray, and will be able to see the structure very clearly, but you must be careful to touch the remains of the bone very lightly, as it will easily crumble to pieces.

Again, take another piece of bone which has not been cooked, and place it in an old cup or jar ; buy at a druggist’s a little “ muriatic acid,” mix with about twice its quantity of watei’, and pour it over the piece of bone. This will gradually dissolve the earthy portion and leave only the gelatine, which will be so soft that it may be easily cut, but it will be of the exact shape of the bone, and if melted down in water would form glue.

The human frame is divided into

The Head,

The Trunk, and The Limbs.

You will of course understand that by the head is meant the skull containing the brain, which is the organ of all the senses.

The Trunk is the part usually called the “ body,”

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and in it are placed the organs by means of which our food is digested, by whicli tlie blood is formed and carried throughout the system, and by whiclx we breathe.

The Limbs are the arms and legs ; and the ends of them — that is, the hands and feet — ^are called the Extremities.

The Skull.^The Skull consists of several bones, which are united in a manner somewhat like the “dovetail’' used by joiners, but it is far more complex, the peculiar mode of joining extending throughout the whole thickness, thus locking the parts together so firmly that it is impossible to separate them ; in fact, additional strength is given at these joints by the bones being thicker there than at any other part. These joints are called Sutures, and are shown in the view of the skull here given (Fig. 1).

Side View of the Skull.

The following are the principal bones composing the skull : — F, the Frontal bone, or forehead. It is this bone which gives a beauty of form and a dignity seen in no other animal in creation. In the skulls of Europeans, the forehead and front of the face are nearly in an upright line, which, you

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will see, is very dilFerent in the lower animals, such as the Orang (Fig. 2) and the Chimpanzee (Fig. 3).

Next are the Parietal bone.s, marked P in Fig. 1. These form the walls of the skull, and meet at the crown. They join the Temporal bones, T, which form the sidd§ at the part of the head known as the tem2)les ; and at the back and lower part of the temporal bone there is a hole, outside of which the Ear is placed. This opening is the entrance to a canal which is hollowed out in the bone, and in which the organ of hearing is placed ; from this the nerve passes which conveys sounds to the brain.

As I intend giving you a lesson on the Ear and the sense of hearing, I will not say more on that subject in this place.

The parietal bones join the Occipital, which forms the back and base of the skull.

Returning now to the front of the head, we observe two large cup-like cavities called the Orbits, in which the eyeballs are placed ; above each of these there is a strong ridge, which is covered by the eyebrow, and this serves greatly to protect the eye (which is a most delicate organ) from injury, as it lies sheltered by the surrounding walls.

At the back of each orbit there is a hole, through

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wliich the nerve of sight carries the form which is reflected on the eye, to the brain, and this is how we see.

At the inner corner of the orbit there is a small canal passing down into the nose } this is called the Lach-ry-mal duct, or tear canal.

To understand the use of this duct, you must be told that above the outer corner of the eye there is a little gland called the “ tear bag,” which, as its name Avill tell you, contains tears.

Glands are soft masses made up of a number of small cells or bags, or of a great quantity of fine tubes twined together ; their use is to secrete — that is, to gather — certain liquids which separate from the blood.

The purpose of the liquid which gathers in the tear bag is to moisten the eyeball as it moves about, and as the eyelids open and close over it.

When this duty has been performed, the surplus moisture passes down the lachrymal canal into the nose ■ but sometimes, owing to pain or deep feeling, a greater quantity of the liquid than is required rushes to the eye ; and as this comes more quickly than it can be carried off by the canal, it overflows and rolls down the face in the shape of tears ; this sometimes takes place from the effects of a cold.

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I shall be able to tell you more about this when speaking of the eye itself further on.

Under the Orbits we have the Cheek Bones, 0 H, which form their lower edge, and between these are the bones forming the upper part of the Nose, N ; the lower part of the nose is not composed of bone, but of cartilage or gristle.

Next, we come to the Upper Jaw, containing, as you know, some of our teeth, the rest being fixed in the Lower Jaw, J, which moves by means of a hinge-joint just in front of the opening of the car.

The manner in which the Lower Jaw works against the upper dilfers according to the habits of the various animals, and the food they live on ; thus, the jaws of the Car-ni-vora (animals which live entirely on flesh, such as the lion, tiger, cat, &c.), have an %vp and doion movement, by which the sides of the back teeth pass closely against each other, and so cut up the meat exactly as sharp shears would do.

But oxen, horses, &c., wliich belong to the group called Herb-i-vora (animals that live on herbs and things which grow), have what is called a. lateral or sideway movement, and thus their food is ground up between their flat-headed teeth as in a mill (in fact, the back teeth in all animals are called molar or mill-like). See page 44.

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You will understand wliat this movement is like if you place your open hands together, as it you were going to clap them, then, keeping the wrists still touching, move the palms from left to right over each other.

But no doubt you have seen a cow taking its meals, and have you not noticed how, when lying on the grass with her eyes closed, the very picture of comfort, she grinds np the grass which she cropped sometime before, and which having been well soaked in her paunch has come up again to be properly chewed? You will then have noticed how the lower jaw moves from side to side, to an extent which would certainly make Miss Pussy’s jaws ache for a long time if she were only to attempt it.

In the Rodents, that is the gnawing animals, such as the beaver, whose mode of building requires it to cut through branches of trees, and the Squirrel, who has to bite through the hard shells of nuts, the jaws do not move sideways, but have a forward and backward action, and as the ridges on their back teeth ai’e set in opposite directions, they act as files, and so grind down the hardest vegetable matter.

Now Man is called an Omnivorous animal, that is, one which can eat any sort of food, whether

5 Lumbral* 1 12 Costal. I 7 Cervical.

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animal or vegetable, and tlms we have the power of moving our jaw in all the ways described. We can cither simply open and shut our mouth, or we can move our lower jaw sideways or forward, just as we desire, thus showing how wonderfully the construction of every creature is adapted to its habits and mode of life.

The Trunk,

The most important portion of the Trunk is the Spinal Column, or, as it is more properly called, the vertebral column, as it is made up of a number of separate bones called vertebrce.

These bones are named according to the phvces they occupy, as follows (Fig. 6)

Fig. 6.

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7 Cervical, or of the neck.

12 Costal, or of the ribs (sometimes called Doi'sal).

5 Lumbral, or of the loins.

As these move on each other by a sort of hinge-joint, they are called the twenty-four movable vertebrae.

They rest on a large flat bone called the Sacrum, S, Fig. 8, which has been made up of five separate vertebrse, but which have now no motion ; and these are followed by four small bones called Caudal, c, or of the tail, also fixed in man ; but in other animals the bones forming the tail are more numerous, and are movable.

The immovable vertebrae, then, are —

5 Sacral, or belonging to the sacrum ;

4 Caudal, or of the tail ;

and you will thus see that the Human vertebral

B

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column consists of twenty-four movable and nine immovable bones ; total. 33.

Eacli separate vertebra consists of a solid piece of bone called the body, B, Fig. 7 ; a back, in wliicb is a canal, or tube, C. Througli tins canal the Spinal Cord, which is a lengthened portion of the brain, passes.

The vertebrje have strong pieces of bone called “transverse processes,” T T, projecting from their sides, and others from their back. These, which you can feel at the back of your neck, are called the “spinous” processes, S; and this is why the vertebral column is sometimes called the sjnrie.

Several large fleshy bands, or cords, the purpose of which is to bend the back, are fixed to these processes. These bands are called muscles, and we shall speak of them in another lesson.

We are protected against any ill effects which might arise from sudden shocks or “jars,” by which the vertebrm might be fractured and the spinal column be injured, by cushions of cartilage (see C, Fig. 8, annexed) placed between the movable vertebrm.

By long pressure of the bones on these cushions they become flattened, and the body thus bends forward. During rest, whilst lying down at night,

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the cushions, being elastic, recover their form, and thus a man is about half an inch taller in the morning than he was when he lay down the night before. In very old persons, however, the pads do not recover their elastic quality, and this will account for the stooping form of the aged.

The annexed drawing (Fig. 8) shows the trunk complete, and from this you will see how all the other parts of the skeleton spring from, and are dependent upon, the vertebral column.

The Ribs are slender but strong bony hoops, which are situated at the upper part of the trunk.

They are twenty-four in number, namely, twelve on each side, and are all attached to those bones of the spinal column which you will remember are called costal vertebrse; but although they are attached^ they are not Jixed^ but work by a joint, the purpose of which will be explained to you in the lesson on breathing.

You can examine how the ribs of animals are attached to the vertebrie when you have a mutton chop j for you know a mutton chop is a rib of a sheep, and a sheep is a vertebrate animal — that is, one having a vertebral column. When you have removed all the mutton, you will find that there will remain a long thin bone, which is a part of a

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rib, and a block of solid bone at the upper end, which is a piece of a vertebra. Now if you clear away all remains of ligament (the bright bluish bands which hold bones in their places) you will be able to move the rib in the vertebra, and in fact, to separate it entirely.

The fourteen upper ribs, namely, seven on each .side, come right round from back to front, and are joined to a flat narrow bone called the Sternum, or breast-bone, S.

The bones of the ribs are not, however, carried quite up to the breast-bone, but they end in cartilage, or gristle, and by this means they are joined. I have marked this joining in the drawing.

These fourteen ribs, which are united to the Vertebrae at the back, and to the Sternum in the front, are called True Ribs.

The next six ribs, that is, three on each side, are attached to the vertebrae at the back, but not to the breast-bone. They come partly round, and then each is joined by cartilage to the one above it ; and the last four ribs (two on each side) are joined at the back only, but are not in any way attached in the front. The whole of these last flve pairs of ribs, that is those which are not fastened to the breast-bone, are called “False Ribs;” and the

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last two pair of these, which are not joined in front at all, are called “ Floating Ribs.”

The twelve Costal vertebrje, the twelve pairs of ribs, and the breast-bone, form the framework which encloses the great cavity or chamber called the Thorax.

In the Thorax are placed the Heart, Lnngs, and other very important organs ; and you will at once see how well all these are protected by the beautifully constructed bony cage by which they are surrounded.

But this framework, although strong, is not rigid, for, owing to the joints at the back, and the cartilage in the front, it can rise and fall so that the space within may become enlarged, and thus room may be allowed for the action of the organs it contains.

The lower part of the trunk is formed by two large bones called the Haunch bones (or hips), H, which join on to the Sacrum. These together form the Pelvis (or basin), in which many very important organs are contained.

The Trunk, then, consists of the Vertebral column, made up of twenty -four movable and nine immovable bones, of seven pairs of true and five pairs of false ribs, and of the haunch bones.

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The Limbs.

The Upper Limbs, that is the Arms, are attached to broad flat bones, called the Shoulder-blades, S, which are triangular (three-sided) in shape, and placed at the back of the ribs. From the upper comer the bone turns round and so forms the shoulder, and into this a bone is joined, called the Clavicle, C, or Collar-bone, the other end of which works in a hollow in the top of the breast-bone.

The name of this bone is derived from that of a key which the Romans used, which seems to have been of this shape. The purpose of the collar-bone is to keep the shoulders apart, and to keep them firm when the upper limbs are being used, hence we find that in animals such as the horse it is absent, for the weight on a horse’s fore-legs (which are his arms) serves to keep them as far apart as is required j in a lion or cat, whose modes of life compel them to squeeze through bushes and to spring and jump, the collar-bone is but very small, and is not fixed, so that tlieir shoulders may not be kept apart ; but in birds not only is this bone very strong, but the two are joined at the bottom so as to form one bone, shaped something like a V> R^d which is known by the name of the Wishing-bone, or Merry-thought, for you know the bird’s wings

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are its arms, and of course in flying these have to be constantly worked, and this could not be done unless the shoulders were kept firmly ajiart. The clavicles enable man to raise weights, and in very many ways give strength and firmness to the arms.

Now you must understand that the bones belonging to the upper limbs correspond with those in the lower, that is, there are the same sort of bones in each. Thus the haunch-bones already spoken of answer the same purpose in regard to the legs which the shoulder-blades do to the arms. At the one end of the shoulder-blade there is a very shallow cup, called the Glenoid cavity, in which the head of the upper bone of the arm works, and on the side of the haunch-bone there is a deep cup in which the head of the thigh-bone moves. The cavity which receives the arm-bone is shallow, to allow of our moving our arm about very freely, whilst the deeper cup in which the thigh-bone moves assists in affording a firm rest for the body, the great freedom of action required by the arms not being necessary for the legs.

The upper bone of the leg, which is called the Femur, or thigh, marked Fern, in Fig. 9, corresponds with the upper bone of the arm called the Humerus, H., in Fig. 10.

of tlie Arm and Hand.

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The heads of both of these are shown in Fig. 8, so that you will be able to see the way in which they are attached to the bones in which they work.

Fig. 9 shows the lower bones of the leg, and Fig. 10 shows the bones of the fore-arm, and you will see that there are the same sort of bones in each, and that as the limbs become more distant from the trunk, they are formed of two bones instead of one ; this gives lightness combined with strength.

The larger bone, T, of the lower leg is called the Tibia ; it is three-sided, and its sharp edge in front is called the shin ; the bottom of this bone forms the inner ancle, and it rests on a large bone in the foot.

The smaller bone attached to the side of the Tibia is called the Fibula, F. and the lower end of it forms the outer ancle.

At the joint of the knee there is a round bone, called the Patella or knee-pan, P, which gives firmness to the leg, and assists in the action of the muscles which pass over it.

The fore-arm corresponds in structure with the lower leg, being formed of two bones, of which the largest is called the Radius, R, and the other the

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Ulna, U. Tlie upper end of the Ulna forms the sharp point of the joint called the Elbow.

The Radius is much lai’ger at the bottom than at the top, and to the larger end of this, the bones forming the wrist are attached.

This bone is annexed to the Ulna in such a manner that it can glide nearly round it, and this gives us the ,power of twisting our hand. Hold your arm out quite straight with the back of the hand uppermost, and you will see that you can turn it so that the palm is upward without Tiwving the joint at the shoulder. It is this motion which is going on in the arm of a carpenter when he is boring a hole with a gimblet or driving in a screw with a screw-driver.

The ends of the limbs, namely, the feet and hands, are called “ Tbe Extremities,” and, as in the limbs, there is the same arrangement in each.

In the foot we have three sets of bones, called the Tarsus or instep (tar), the Meta-tarsus, which forms the front part of the foot (M T), and the . Toes,

In the hand we have the Carpus, C, or wrist, which corresponds with the Tarsus of the foot. Next come the bones of the Meta-carpus or hand (M C), which are similar in aiTangement to the

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Meta-tarsus, and you will easily see that the fingers correspond with the toes.

There are seven bones in the Tarsus, one of which, a very large one, forms the heel, and on the bone over this the Tibia rests.

In the Carpus there are eight bones, all of which are wedge-like in form, the narrow ends being placed inwards ; so that the wrist is shaped like an arch, and whilst it is very strong, it is still capable of the most delicate movements.

The Meta-tarsus consists of five bones, and the Meta-carpus of five ; in fact, these two sets of bones are very nearly alike in shape as well as in number, the inner one of each being rather thicker than the other four.

The toes and fingers correspond exactly in their number and the character of their bones, the great toe holding the same position in the foot as the thumb does in the hand, and each of these has one bone less than the other toes and fingers j thus each of the toes is made up of three bones, whilst the great toe has but two, and each of the fingers is composed of three bones, but the thumb has only two.

The foot of man, is indeed, very wonderful in its construction, being formed on the true arch principle (which you may perhaps recollect I explained to you

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in another little book called “ Our Houses”). All the bones of the Tarsus are like so many stones in the arch of a bridge, and thus press closer together when the weight of the body rests upon them, the piers of the arch (that is, the parts on which it rests) being formed by the toes in the front and the heel at the back. This arch is not only very strong, but, owing to the toes being formed of several bones, the whole foot is elastic, and forms a spring by which the body is moved forward without the other bones being shaken or jarred against each other. In animals whose mode of life renders it necessary that they should bound after their prey, and jump or spring from trees and other high places, this elastic character is increased, and they are provided with pads under each joint, which serve to break the shock their frame would otherwise receive. I have no doubt that you have noticed how very quietly and nimbly a cat runs, and if you could manage to examine her paws when she has “ gloves on,” you would see that this is owing to little black cushions which she has under them.