Part 234

BOOK OF THE HUMAN BODY

WHAT THE HUMAN BODY IS

ITS DIVISIONS AND SYSTEMS

GENERAL STRUCTURE OF THE BODY

FRAMEWORK: BONES, MUSCLES AND CELLS

THE DIGESTIVE SYSTEM AND ORGANS

CIRCULATION OF THE BLOOD AND RESPIRATION: HEART, BLOOD VESSELS, LYMPHATICS, LUNGS AND BRONCHII

THE EXCRETORY SYSTEM: INTESTINAL TRACT, KIDNEYS, SWEAT GLANDS, LUNGS

THE NERVOUS SYSTEM: NERVES, BRAIN, SPINAL CORD

ORGANS OF SPECIAL SENSE: EYE, EAR, NOSE, TONGUE, HAND AND SKIN

CHARTS, TABLES AND SPECIAL FEATURES

BOOK OF THE HUMAN BODY

The study of the Human Body involves numerous other branches of science, and, as a whole, is the most complex and intricate of all the sciences. To explain its structure and workings we apply the principles of Biology, Physiology, Chemistry, Physics, Psychology, and Metaphysics.

The individual man, as a whole, is frequently forgotten both in physiology and in medicine, owing to the extraordinary minuteness and exactness with which each part and organ is examined and described. At the outset, then, it should be remembered that the human body is an organic whole, and what makes it _one_ is not the similarity or unity of the machines and processes, for they are unlike and many; but it is the unity of the one governing force, the _mind_, and especially the _unconscious mind_, which presides over the body.

Nothing in the body is merely mechanical, although there is much mechanism; all is vital, all is united in one great aim--the health and well-being of the individual.

All organs and systems are held together and formed into one body by means of a framework, partly fixed and partly movable, partly rigid and partly flexible, partly hard and partly soft.

The _skeleton_ part of the framework is made of _bone_; flexibility is given to certain parts by means of joints, which are simply smoothed and rounded ends of bone covered with gristle to avoid friction, and joined together by fiber and ligament for strength. This forms the rigid and hard parts of the framework.

The flexible and soft part, which everywhere covers organs and muscles, is composed of a layer of fat to preserve the warmth, as fat is a non-conductor, and an outer covering of skin.

This framework is exquisitely adapted to give strong protection to the vital parts so that they cannot readily be injured; and the whole of the organs are so arranged and stowed away that a perfect human body is a beautiful object full of symmetry and graceful curves and lines.

=Divisions of the Body.=--If we divide the body into six parts--four limbs, trunk, and head and neck--we find each part contains about thirty bones (counting the ribs in pairs) there being about _two hundred_ in the entire body.

The height of the body depends mainly on the length of the bones of the lower limbs.

=Everything in Pairs.=--In the body almost everything is paired, right and left, giving it symmetry. There are but five central bones: two in the head, one in the throat, and the breastbone and backbone (or spine); and there are but five single muscles, all the rest--out of many hundreds--being in pairs. In the interior, where economy rather than symmetry is required, it is not so; there being as many single organs as there are double.

=The Body Viewed as a Machine.=--A favorite way of looking at the body as a whole is to regard it as an anatomical machine. In this view the body has an internal skeleton, of which the chief feature is the central axis or backbone.

Considering the skull and backbone as one, the body may be said to be built up of two tubes. The smaller posterior or neural tube includes the cavity of the skull and the vertebral canal. Within this tube is lodged the nervous center, or engine, of the body. The anterior, or body, tube is much larger, consisting of the face above, and the neck and trunk below, and it contains the _four nutritive systems_ of life, so that the whole body in section is like an eight with the lower circle immensely exaggerated. The limbs, of course, are not tubular, and merely form part of the machinery.

Adopting the simile of the human engine and boiler and machinery, we see that the limbs, etc., are the machinery; the posterior tube the engines and force that move them; and the anterior tube the human boiler that generates the force. This boiler, like one in a steam engine, has an upper and lower part. The upper part is where the steam is generated (in lungs) and sent to the engine (the brain) by the heart. The lower part is where the fuel is burned (the stomach) and the ashes and refuse drop through (the intestines). So that the analogy between the two is close and striking.

=Centers of Control.=--There are two distinct seats of government in the human body: the one in the _upper brain_, or cortex, the other principally in the very center of the human body. That in the upper brain, or cortex, is the human will and the conscious mind. It has absolute control given to it over the animal part of the human life--that is, over the part that consists in the using of force, which includes the nervous and locomotor systems, and the special senses.

_Nutritive Systems._--The other government, situated in the lower part of the brain and spinal cord and in the center of the body--in front of the spine and behind the stomach--is of an entirely different order. To put this more plainly: The four systems that lie in the body--_digestive_, _circulatory_, _respiratory_, and _excretory_--may be termed the nutritive systems, being designed for the maintenance and storage of life-forces. They are almost entirely under the control of the involuntary nerve centers, and have full and undisputed sway over life itself--that is, over the generating and storing of vital force, rather than over its usage.

SYSTEMS AND ORGANS OF THE BODY

=How the Body is Built.=--In a building such as the body it is well to begin with the _unit_--the building unit. In a house this is a brick or a stone; in all living structures, animal and vegetable, it is a _cell_.

All living structures, whether animal or vegetable, are built up of cells (which we shall consider in due course), and these cells are grouped together for different purposes to form different tissues. The _tissues_ are the different materials of which the body is made. There are eight principal tissues in the body: _bone_, _gristle_, _muscle_, _nerve_, _skin_, _fat_, _fiber_, and _connecting tissue_.

(1) The _Osseous_, or bone tissue, is the framework of the body. This material is found, of course, in every part of the body and forms the skeleton.

(2) The _Cartilaginous_, or gristle, forms the joints of the body. This tissue covers the ends of the bones to form the joints; it unites the ribs with the breastbone; it forms the rings of the windpipe and the lid of the larynx at the back of the tongue; the lower part of the nose, the upper eyelid, and the ear.

(3) The _Muscular_, or muscle, forms the machinery of the body. This tissue covers all the bones with flesh, which is muscle, and is the chief part of a number of machines by which every movement is performed. It is also an important tissue in the wall of the abdomen and the floor of the chest.

(4) The _Nervous_, or nerve tissue, is the moving power of the body. It is the chief constituent of the brain and the spinal cord, inside the backbone or spine. It also forms the nerves, which run like white threads from the brain to all the muscles, and give them power to move.

(5) The _Epithelial_, or skin, forms the outer covering of the body. This tissue is the skin that covers the body outside, and lines it as mucous membrane inside, and also forms the teeth and nails.

(6) _The Adipose_, or fat, forms the under covering of the body. This tissue is the inner protective sheathing and padding of the body, beneath the skin, and round the internal organs. It consists of drops of oil, enclosed in separate cells.

(7) The _Fibrous_, or fiber or sinew, is the tissue that forms the cords and bands of the body. This tissue makes the strong tendons that fasten the muscles to the bones, and forms the covering or sheath of the bone itself, and the various organs.

(8) The _Connective_, or cementing tissue, joins all the parts and cells of the body together. This substance is found everywhere, all over the body, and is like the mortar in a house, fastening all the bricks together. It is a sort of network of cells and long fibers.

=Special Systems.=--These eight tissues are combined together into various groups of _organs_ or _systems_ for special purposes. These groups are six in number, and include: the _circulatory_, _respiratory_, _digestive_, _excretory_ or _secretory_, _locomotor_, and _nervous systems_. There is also the _reproductive_ system, which has to do with the propagation of the race, and involves many important and vital questions.

We may divide these six into three groups:

There are two in the chest:

(1) The _Circulatory system_ is that by which the blood or liquid food is distributed throughout the body to all the tiny cells. This system includes the _heart_ or force-pump, and the _arteries_, _capillaries_, and _veins_ or the three kinds of pipes through which the blood travels.

(2) The _Respiratory_ system is that by which we breathe, and by which the body is fed with oxygen, which gives the blood its bright red color. This system includes the nostrils and mouth, the windpipe and the lungs.

Then there are two in the abdomen, or stomach:

(3) The _Digestive_ system, by which all the food is made into liquid and changed so as to nourish the body and pass into the blood. This system includes the mouth, gullet, stomach, liver, pancreas, intestines, and other organs.

(4) The _Secretory_, or excretory, system (for they are best grouped as one) manufactures the various fluids of the body, such as bile, urine, sweat, saliva, gastric juice, etc. It consists of various glands or secretory organs in different parts of the body, such as those in the skin, the kidneys, the lymphatic glands, the spleen, etc. It also gets rid of the refuse of the body.

Lastly, there are two in the head and limbs:

(5) The _Locomotor_ system, by which all movement is effected. This includes the bones, joints, and muscles.

(6) The _Nervous_ system, by which all the body is controlled, directed, and regulated. This system includes the brain, spinal cord, and the special senses, such as the ear, the eye, and all the nerves.

=The Human Chest, or Thorax.=--In it, the blood is purified and circulated. The _thorax_ is closed above and below: above, by the neck, through which the windpipe enters it in front, conveying air to the lungs; and by the _gullet_ behind, conveying food to the stomach. Below, the floor, dividing it from the abdomen beneath, is formed by a very large muscle stretching right across the body, called the _Diaphragm_, or partition wall; also called the _Midriff_. The thorax is walled in at the sides by the ribs, and behind by the backbone in which is the other tube that contains the spinal cord. The thorax contains the two organs of _respiration_ and _circulation_.

The _lungs_ are the organs of respiration. They are like two sponges filling the right and left halves of the chest. Wherever you can feel a rib there is part of the lung underneath. Each of these lungs is contained in a bag, like a skin, that separates it from the ribs, and is called the _pleura_ (from _pleuron_ = a _rib_), but the lung is not _inside_ the bag.

The _outer_ layer of the pleura is fixed to the side of the chest, the _inner_ layer to the lung, and the two layers move on each other like a joint when we breathe.

The lungs are full of small air-cells with minute tubes leading from them. These gradually increase in size as they join together, till at last they unite in one large tube, or bronchus, for each lung. These two bronchi join together, and form the _windpipe_, or _trachea_, which conveys the air through the larynx into the mouth.

The windpipe is kept stretched widely open by a series of elastic rings of gristle. Behind the windpipe is the gullet, leading to the stomach.

We take air into the lungs to pass thence into the blood, and thus be carried to all the cells of the body to enable them to live and breathe.

=The Heart.=--The _heart_ is at the lower part of the chest, between the two lungs. It is a _fleshy_ or muscular organ, about the size of the fist--flat above, and pointed below like a sugar-loaf. It lies in a slanting direction behind the breastbone--the broad part, or the _base_, of the heart being upwards and partly to the _right_ of the breast-bone; the point, or apex of the heart, being downwards and to the _left_, where it can often be seen beating against the chestwall.

The heart is hollow, and acts like a pump, forcing the blood all over the body through the great vessel that leaves the heart at the upper part. The heart, like the lungs, is enclosed in a double layer of folded bag, called the _pericardium_, because it is round the heart.

The _gullet_ runs right down the back of the thorax, and passes out through the diaphragm, which forms the floor, into the abdomen.

The _abdomen_ forms the lower half of the trunk, and is often called the _stomach_. It is full of organs belonging to the _digestive system_ and _secretory system_, by which the fuel or food is rendered fit for use in the blood and the body.

The _walls_ of the abdomen are not protected by ribs like the thorax, but are all formed of flesh or muscle. The principal organs they contain are the _stomach_, the _liver_, the _pancreas_, or _sweetbread_, the _spleen_ or _milt_, the _kidneys_, the _intestines_, and the _bladder_.

=The Human Brain.=--The _head_ and _spine_ contain the principal nervous systems of the body and four organs of special sense--_sight_, _hearing_, _smelling_, and _tasting_.