Chapter I: The Anglo-Saxon Period, 449-1066 (19)

The thickness of the deposit, providing the supply of the metallic solution be kept constant, will depend on the _length of time the object is exposed to the influence of the battery_.

ELECTRO-MAGNETISM

_What is electro-magnetism?_

It is the magnetism developed through the agency of _electrical_ or _galvanic action_.

_What were the earliest phenomena observed which indicated a
relation between magnetism and electricity?_

It was noticed that _ships’ compasses_ have their directive power impaired by lightning, and that sewing needles could be rendered magnetic by electric discharges passed through them.

_What discovery, made by Prof. Oersted of Copenhagen, established
beyond a doubt the connection of electricity and magnetism?_

He ascertained that a magnetic needle placed near a metallic wire connecting the poles of a galvanic battery was compelled to change its direction, and that the new direction it assumed was determined by its position in _relation to the wire_ and to the direction of the current _transmitted along the wire_.

Thus, if a needle be inclosed in a wire not touching it at any point, and a current of electricity pass through the wire, the needle will be made to move in accordance with the direction of the current.

_What other important discovery was made about the same time?_

It was found that if a piece of soft iron, not possessing magnetic power sufficient to elevate a grain weight, be placed within a coil of copper wire through which a galvanic current is passing, it will become, through the influence of the current, a _powerful magnet_; and will, so long as the current flows, sustain weights amounting to many hundreds of pounds.

_Is the magnetic power of the bar found to be wholly dependent on
the existence of the current?_

It _is_; the moment the current stops, the weights _fall away_ from the bar in obedience to the law of gravity.

_How great weights have been lifted by magnets formed in this
manner?_

An electro-magnet constructed by Prof. Henry was capable of elevating and sustaining about a _ton weight_.

_Upon what principle does the construction of the Morse magnetic
telegraph depend?_

Upon the principle that a current of _electricity_ circulating about a bar of soft iron is capable of _rendering it a magnet_.

_Why is it necessary, in conveying the telegraph wires, to support
them upon glass or earthen cylinders?_

These are used for the purpose of insuring the perfect _insulation_ of the wires, since but for this the electricity would pass down a damp pole to the earth, and be lost.

_Is there any truth in the idea that many persons have, that some
principle passes along the telegraphic wires when intelligence is
transmitted?_

This supposition is _wholly erroneous_; the word current, as something flowing, conveys a false idea, but we have no other term to express electrical progression.

_How can we gain an idea of what really takes place, and of the
nature of the influence transmitted?_

The earth and all matter are _reservoirs of electricity_; if we disturb this electricity at Boston by voltaic influence, its pulsations may be felt in Chicago. Suppose the telegraphic wire were a tube, extending from Boston to Chicago, filled with water. Now, if one drop more is forced into it at Boston, a drop must fall out at Chicago, but no drop was caused to pass from Boston to Chicago. Something similar to this occurs in the transmission of electricity.

_What was the earliest important industrial application of
electricity?_

One of the earliest industrial applications of electricity was to the driving of street cars. The first electric railway was installed by Siemens, of Berlin, in 1882; and the system was quickly taken up and brought to a high state of development by American engineers. It is remarkable that the system of traction early adopted is the one generally used in America and Europe until the present date. It consists essentially of (_a_) a supply of _continuous current_ at five hundred to five hundred and fifty volts, generated in (_b_) a _central powerhouse_, and transmitted to the car by means (_c_) of _overhead conductors_, whence by contact with a trolley wheel on a pole on the car it is led down to (_d_) _two series-excited motors_, which are placed electrically first _in series_ with one another _at starting_, and then _in parallel_ with one another when a sufficient speed has been attained.

_To what well-known electrical machines did this give impetus?_

Electric _dynamos_ and motors. All such machines will convert the energy of mechanical motion into that of electricity in motion, or the reverse. The former conversion is done by _dynamos_, to which power is given by steam-engines or other such prime-movers, and made to generate in conducting circuits alternate or direct currents of electricity. _Motors_, on the other hand, receive the energy of electrical currents, either alternate or direct, and this produces motion of certain parts of the structure.

The theory of the action of a dynamo was first discovered by Faraday in 1831; it is intimately associated with that of a motor, for the principle of conservation of energy points out that either machine is reversible--that is to say, a dynamo may be used as a motor or a motor as a dynamo, though perhaps not so efficiently as when each fulfills the special function for which it was designed.

THE CURRENT IN A DYNAMO OR MOTOR.--This brings us to the production of an electric current by the dynamo. In the dynamo we have a coil of wire moving across a magnetic field, alternately passing into this field and out of it. A magnetic field is produced, as we have just seen, by the steady movement of electrons, and we may picture it as being a region of the ether disturbed or strained by the effect of the moving electrons. When the coil of wire passes into the magnetic field, the electrons of its atoms are influenced powerfully and set in motion in one direction, so producing a current in the coil. As the coil passes away from the field, its electrons receive a second impetus, which checks their movement and starts them traveling in the opposite direction, and another current is produced. The coil moves continuously and regularly, passing into and out of the magnetic field without interruption; and so we get a current which reverses its direction at regular intervals, that is, an _alternating_ current.

THE MORSE DIRECT INKING PRINTER

THE MORSE SOUNDER]

A .-
B -...
C -.-.
D -..
E .
F ..-.
G --.
H ....
I ..
J .---
K -.-
L .-..
M --
N -.
O ---
P .--.
Q --.-
R .-.
S ...
T -
U ..-
V ...-
W .--
X -..-
Y -.--
Z --..
1 .----
2 ..---
3 ...--
4 ....-
5 .....
6 -....
7 --...
8 ---..
9 ----.
0 -----

THE MORSE TELEGRAPH CODE FOR LETTERS AND FIGURES

_What are some of the chief modern applications of electricity?_

The field of applied electricity is one of the most extensive in modern science, invention and industry. Electricity in some form is now utilized in connection with lighting, telegraphy, the telephone, heating, motor boats, railways, aëroplanes, in metallurgy and the arts, clocks, bells and alarms, wireless telegraphy and telephony, submarine telegraphy, automobiles, cooking and domestic science, in medicine and in military science.

_Give a brief account of wireless telegraphy._

In the case of ordinary telegraphy we always make use of extended metallic wires or conductors from the place from which the message is sent to the neighborhood to which it is desired to send it. In the case of _wireless_ telegraphy no such conductors exist.

Among the most interesting of the many systems of wireless telegraphy now in vogue the modern Marconi, the De Forrest, the Fessenden, and the Poulsen are noteworthy. It is, however, with the name of Marconi that the introduction of wireless telegraphy will always be directly associated.

In 1888 Hertz had demonstrated in a remarkable series of experiments the existence of electro-magnetic waves, and had even shown how these might be produced, detected, and made to exhibit all the chief phenomena of wave-motion. Marconi’s great achievement lay in so controlling and regulating the dispatch and receipt of such waves as to make them record signals on a specially designed apparatus in accordance with the well-known Morse telegraphic system. His method, as first patented in 1896, was briefly as follows:

THE TRANSMITTER, by which the electromagnetic waves were generated and sent off into space in all directions, consisted of a battery connected through a key to the primary of an induction coil whose secondary terminals were joined to two brass balls between which there was a short air-gap. From one of these balls a wire was taken to earth, and from the other an aërial wire was led some distance up in the air. The closing of the primary circuit led to sparks passing across the air-gap, which produced electro-magnetic waves in the ether in exactly the same way as the dropping of a stone into a pool produces a series of concentric ripples.

THE COHERER.--To receive and interpret these waves Marconi employed a “coherer” in circuit with a battery and having connection with an aërial wire on the one side and an earth wire on the other. The coherer consisted of a small glass tube not more than, say, two inches long by one-quarter inch in diameter, into the ends of which were fused two platinum wires leading to small metallic electrodes. These electrodes were brought quite near each other, and in the narrow gap between them was placed powdered metallic silver, antimony, etc. The resistance offered by this powder was so high, on account of small air-gaps between the particles, that no current could pass through.

Electro-magnetic waves, however, possess the peculiar property of breaking down the resistance of this powder whenever they impinge upon it. Hence as soon as a wave reached the coherer, the resistance practically vanished and a current passed round the circuit. It was a mere detail to arrange that this current should actuate a relay connected with a telegraphic instrument which would record the signal, and that a hammer would at the same time tap the coherer so as to agitate the powder and “decohere” it, setting up the resistance again for a fresh signal.

IMPROVEMENTS.--Since this system was devised many most important improvements have taken place. One of the most noticeable of these was Sir Oliver Lodge’s invention of tuning and syntonizing apparatus by which a transmitter and receiver are tuned to the same periodic oscillation, and thus a number of messages might be operated in the same field without interference. Lodge accomplished this to some extent by adding inductance coils and condensers to the circuits. Various other methods have been adopted to secure syntonization; but the resonance effects obtained are not great enough to make selective signaling certain.

THE GENERATOR.--In the modern Marconi system the energy for the transmitter is obtained from a generator working at one hundred and ten volts. The current is led through a key and an improved form of interruptor to the primary of the induction coil, whose secondary terminals communicate with the spark-gap. The spark-gap is in series with a condenser and the primary of a high tension transformer, of which latter one secondary terminal leads to the aërial and the other to the earth wire.

THE DETECTOR.--In the receptor the metallic coherer has been discarded for a magnetic detector. This instrument consists of a small glass tube through which travels an endless band of iron wires, moving round two grooved pulleys. Close to the tube are two permanent magnets, and round it is wound a primary coil consisting of one layer of wire. One end of this coil is led straight to earth; the other passes through a condenser to a tuning inductance coil leading in one direction to earth and in the other to the aërial. Above the primary coil on the glass tube a secondary coil is wound and connects with a telephone receiver. The action is simple. The electro-magnetic waves, reaching the aërial, set up oscillatory currents in the primary which act upon the magnetic field. Currents are thus generated in the secondary, which record the message in the telephone receiver by a series of taps corresponding to the Morse dashes and dots.

=TELEPHONING FROM NEW YORK TO SAN FRANCISCO BY WIRELESS=]

The _De Forrest system_ is very largely used in the United States, Japan, and elsewhere, and in its more recent modifications secures a high efficiency by means of a number of ingenious improvements.

_Describe the wireless telephone._

As in wireless telegraphy, all modern systems of wireless telephony are based upon the action of electro-magnetic waves. It is impossible here to discuss all the various methods that have been devised, but the leading principles employed may be indicated, with special reference to some of the best-known systems. They may be classified according to the methods in which the waves are produced.

SPARK DISCHARGE SYSTEMS.--These rely for the generation of the Hertzian waves upon a spark discharge across an air-gap. The _De Forrest system_ is perhaps the most popular of this type. In this system the spark discharge is utilized to produce waves of a frequency not less than one hundred thousand per second, the resulting sound being inaudible at the receiving station.

A microphone transmitter is employed with this apparatus. When the operator speaks into the transmitter, the variations of resistance act upon the waves in such a way as to produce a new series of waves of such frequency as to be audible at the receiver.

The receiving apparatus includes the usual antenna, and closed secondary circuit, comprising an inductance and a variable capacity, across the terminals of which an Audion delicate detector is introduced. This instrument depends upon the motions of the ions in a rarefied gas. It is one of the most sensitive detectors yet invented, and offers the great advantage of a practically total absence of time lag in recovery.

SINGING-ARC SYSTEMS.--Duddell’s discovery of the singing arc in 1909 has been quickly followed by its application to radio-telephony and radio-telegraphy, first by Poulsen and subsequently by Fessenden, Stone, De Forrest, and others. Under certain conditions the electric arc can be made to emit a musical note, while at the same time it transforms a portion of the energy of its own direct current into oscillations. These are led into an oscillation circuit containing a condenser and inductance, and associated with an antenna and earth line. The microphone transmitter may be included in a circuit associated with the inductance, in which case the voice acting on the resistance of the transmitter causes variations in the oscillating currents; or it may be associated with some part of the direct-current circuit, in which case it acts by affecting the current passing across the arc.

Any form of receiver may be used with this arc apparatus. The great advantage of this method is that the arc produces continuous oscillations of constant amplitude, and that the wave-length and frequency of the oscillations are subject to better regulation and control.

ADVANTAGES.--The advantages of wireless telephony over wireless telegraphy are many. One is that no skilled operator is required to translate the dot-and-dash signals; for in the latter one hears only long and short buzzes, whereas in the former one hears the actual spoken words. By means of wireless telephony the transmission of intelligence is far more direct and expeditious, and in times of emergency this not unfrequently becomes a very vital question indeed. An important characteristic of wireless telephonic communication is the exceptional clearness of the articulation, owing to the absence of the electrostatic capacity of metallic lines and cables which is always present in wire telephony.

Stronger currents, improved sending and receiving apparatus, and the application of new principles have now greatly extended the speaking range; and only recently distinct communication has been established by wireless telephony between New York and San Francisco. The use of the wireless telephone will be greatly extended, especially in naval, military, and shipping communication.

THE MARVEL OF X-RAYS

_Röntgen or X-Rays_, the most famous, and up to now by far the most useful, kind of rays associated with high vacuum tubes, were discovered by Professor W. K. Röntgen in 1895. His first observation was that a photographic plate, which was enclosed in an opaque material and which was lying by chance near the apparatus, was affected just as if it had been exposed to ordinary light. This caused him to conclude that the effect must be due to some unknown kind of rays, and the uncertainty as to their character led him to provisionally apply to them the name of X-rays, for _x_ in algebra generally denotes the unknown quantity.

The later sensational part of his discovery was that the property possessed by a highly exhausted bulb of glass, fitted with suitable electrodes, sends out rays or electric discharges capable of passing through many bodies which are quite opaque to ordinary light, and of either affecting a photographic plate or causing a screen coated with certain chemicals to fluoresce or light up under their influence.

_How are X-rays produced?_

X-rays are thus produced by the discharge of a high-potential current through a special form of vacuum tube, known as a Crookes’ tube. The positive terminal of an induction coil or Wimshurst machine is connected to the anode and the negative to the cathode of the tube. The anticathode is connected to the anode and is also positive. The vacuum of a tube is not perfect, and the current is conveyed through the tube by the infinitesimal quantity of air contained therein.

The “cathodal rays” which pass from the cathode to the anticathode consist of infinitesimal particles traveling at a high rate of speed; when the progress of these minute bodies is arrested, X-rays are produced. The green fluorescence on the sides of the tube opposite the anticathode, though not caused by the X-rays, demonstrate their presence.

WHAT THE X-RAYS ARE.--The X-rays are ethereal vibrations traveling with much the same velocity as light. They travel in a straight line in all directions from the point of origin, and are almost incapable of reflection or refraction.

X-rays are invisible to the eye, but have the property of rendering fluorescent certain substances--for example, calcium tungstate and barium platino-cyanide. When a screen coated with these substances is placed near the X-ray tube in a darkened room, the tungstate or barium surface emits a fairly bright fluorescence. If an object such as the hand or a lead pencil is placed between the screen and the tube, the denser parts (the bones or the graphite) appear as black shadows in a gray background.

X-rays penetrate all substances to a greater or less degree, although heavy metals, such as lead and mercury, are, for photographic or visual purposes, practically opaque to the rays.

The greater part of X-ray examination is conducted by photographic methods, as the image given by the rays on a dry plate or film show far more detail than can be seen by visual examination with the fluorescent screen.

APPARATUS.--The apparatus required consists of a suitable source of electrical energy, such as a battery or dynamo, etc., and a powerful induction or a large electrostatic influence machine, combined of course in either case with an X-ray tube and special X-ray photographic plates. Ordinary photographic plates can be used, but do not give such brilliant results. If we wish to take a radiograph of the hand, we must first of all use a plate slightly larger than the hand, and enclose it in an opaque envelope. Two such are usually employed, one red and the other black. This is placed on the table or stand, film side uppermost, and the hand is placed upon it, and a short distance above the hand is located the X-ray tube. Since what we really take is a shadowgraph picture, to give a good sharp outline, the hand should be placed as flat as possible on the plate, and the tube some six to eight inches from it.

With some of the most powerful apparatus now in use, even the human trunk can be radiographed in a single flash, which is an improvement on the exposure necessary in the early days of its use, when ten, twenty, or even forty minutes’ exposure was no uncommon practice.

THE FLUORESCENT SCREEN.--When the X-rays impinge on certain substances they cause them to light up or “fluoresce” under their action. The number of bodies or chemicals which do so is very large, but for practical purposes only one or two are of any use. The best, and the one always employed, is a chemical known as barium platino-cyanide. The screen-holder consists of a box, preferably of pyramidal form, with a flattened apex or top. Inserted in this apex are two tubes, like opera-glass tubes but without lenses; through these we can look into the box in such a manner as to prevent any outside light from entering. The bottom of the box consists of the screen proper, a piece of cardboard or other suitable substance, one side (the inner) of which is coated with the substance mentioned above, because the light rays given off by the barium platino-cyanide under the action of the X-rays cannot of course penetrate an object opaque to light. The box should be absolutely light-tight except for the eye-tubes.

If such a screen be held in the neighborhood of an X-ray tube, opposite the most brilliantly phosphorescing half of the tube, it will be found to be lighted up under the action of the X-rays. If now we place between the tube and the screen an object such as the hand, putting it in as close proximity to the tube as possible, we obtain a shadowgram on the screen, varying in intensity according to the relative transparency of the different parts of the hand to the X-rays. Since the bones are far less transparent than the flesh, they cast a much denser shadow and are very distinct. On such a screen it is possible to see the beats of the heart, the rising and falling of the diaphragm, etc.

X-RAYS AT WORK.--In medical X-ray work, the patient is placed upon a couch consisting of a wooden frame covered with canvas. A box containing the tube moves on wheels and rails beneath the couch; it is lined with metal to shield the operator from the X-rays. The time of exposure depends upon the strength of current used, the power of the coil, and the condition of the tube. A “hard” tube--that is, a tube with an extremely high vacuum--requires less exposure than a “soft” or low-vacuum tube.

The condition of the tube is ascertained by finding its “equivalent spark gap.” While the coil and tube are working, the terminal points of the induction coil are slowly brought together. If a spark passes between the points while they are six inches or more apart, the vacuum is too high. If no sparking takes place between the terminals till they are within three inches of each other, the tube is low. A good working spark gap distance is four and one-half inches. A soft, or low-vacuum, tube gives better definition than a hard, or high-vacuum, tube, as the rays pass less easily through dense substances and show greater differentiation of tissue. A very high vacuum tube may show but little difference between the bones and flesh, while a soft tube should give the minute structure of the bones.

TIME OF EXPOSURE.--With a current of five amperes at one hundred volts passing through the primary winding of a ten-inch coil, the exposure for a hand or foot would be from three to fifteen seconds. The exposure for the thicker portions of the body would be from twenty seconds to two minutes. If an electrolytic break is used, about half the exposure would be required. Dry plates with extra thick sensitive films are specially prepared for radiography, the development and fixation being the same as in ordinary photography. The image is sometimes barely visible on the surface of the plate during development, but when fixed the negative may give good density and definition owing to the penetration into the film of the X-rays.

KINDS OF X-RAYS.--It is now known that these rays are not all by any means of the same kind or of the same penetrative power. Moreover, these differences can be still augmented by altering what is known as the induction in the circuit, the degree of exhaustion in the tube, and the nature of the emitting surface. The emitting surface is not the glass walls of the tube, as many suppose; and the canary colored light emitted by the tube is not the X-rays, which are themselves invisible. They originate from the anode of the tube owing to the fierce bombardment to which the cathode rays subject it. Where the cathode rays, which travel in straight lines, first strike any material object, from that same object the X-rays originate.

USES OF X-RAYS.--In the early days of radiography the X-rays in medical work were confined almost solely to the detection of fractured or injured bones, and abnormal bone growth. At the present time, however, even a careful examination on the fluorescent screen is sufficient to enable an expert medical radiographist to diagnose with a considerable degree of exactitude the condition of the heart, the lungs, and the stomach. In making such examination a tube must be chosen which has the lowest vacuum, in order to obtain the maximum amount of contrast between fleshy tissue not differing greatly in density.

In some cases even the liver has been outlined and part of the kidneys.

Still more important is the fact that the rays have been applied successfully in the treatment of certain diseases which by other means have been deemed, if not incurable, at any rate extremely difficult to cure. Claims have been made for cancer cures by means of these same rays; whether these have really been complete cures or not is perhaps open to question.

X-RAY DERMATITIS.--A painful and incurable disease, of a cancerous nature, to which radiographers are liable, caused by frequent and prolonged exposure to X-rays. Many of the pioneers of radiography have fallen victims to this complaint, but greater precautions are now taken to protect the operators from the X-rays. There is little danger of contracting this disease in X-ray photography, as the exposures are short and the operator need not stand directly in front of the tube. The chief risk is entailed by visual examination with the fluorescent screen. The disease first makes its appearance in the hands and gradually spreads to the arms and body. The skin at first appears as if it had been burned, hence the term “X-ray burning.”

Illustration and diagram showing the apparatus ordinarily used in X-ray photography, together with the course of the electric circuits, and a radiograph of the hand.]

=LIQUID AIR AND ITS MARVELS OF LOW TEMPERATURE=

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

PRINCIPAL BONES OF THE BODY

1. Collar Bone. (Clavicle)
2. Breast Bone. (Sternum)
3. Ribs.
4. Arm Bone. (Humerus)
5. Lumbar Vertebra.
6. Haunch Bone. (Pelvis)
7. Ulna.
8. Radius.
9. Wrist. (Carpus)
10. Metacarpus.
11. Phalanges.
12. Thigh Bone. (Femur)
13. Knee Cap. (Patella)
14. Brooch Bone. (Fibula)
15. Shin Bone. (Tibia)
16. Tarsus.
17. Metatarsus.
18. Phalanges.

PRINCIPAL MUSCLES OF THE BODY

1. Sternoclidomastoid (the muscle that bends the head).
2. Trapezius.
3. Pectoralis (chest muscle).
4. Deltoid (arm lifting muscle).
5. Coraco brachialis (rudimentary arm muscle).
6. Triceps (forearm extension).
7. Pronator radii teres (turns forearm and hand).
8. Annular ligament of wrist.
9. External oblique of abdomen.
10. Muscular sheath of abdominal erectus muscle.
11. Tensor fasciæ latæ (fibrous muscle covering thigh muscles).
12. Gluteus (controls thigh and helps to keep body erect).
13. Sartorius, or tailor, muscle (enables legs to be crossed).
14. One of quadriceps extensor cruris muscles.
15. Gastroenemius (bends the knee).
16. Long extensor of toes.
17. Peroneus longus (helps to keep foot arched).
18. Annular ligament of ankle.
19. Platyama.
20. Brachialis (moves elbow joint).
21. Biceps (flexor of arm).
22. Supinator longus (turns hand).
23. Extensor carpi radialis (extensor of forearm and wrist).
24. Flexor carpi radialis (bends wrist and turns hand).
25. Rectus abdominis (retracts abdominal wall).
26 and 27. Vastus externus and internus.
These, with 14 and an abductor muscle,
together make up the quadriceps extensor,
the largest muscle in the body. It extends
the leg.
28. Tibialis (extends the ankle).
29. Extensors of the toes.

The bones which make up the framework of the body are held together by joints of different kinds which allow of widely varying ranges of motion. The skull, which contains twenty-two bones in all, includes the cranium which contains the brain, and the bones which form the framework of the face. The vertebral column, which acts as a hinged and pliable tube down the center of which runs the spinal cord, is made up of twenty-four true vertebræ and the sacrum and the coccyx. The thorax, the bony box or cage protecting the heart and lungs, is made up of the twelve dorsal vertebræ with the twelve ribs on each side and the sternum or breast bone in front. The upper extremities consist of the shoulder-blade or scapula, the collar-bone or clavicle, the humerus or upper arm bone, the two fore-arm bones (radius and ulna), and the twenty-seven bones of the hand and wrist. The pelvis is composed of the two hip bones, together with the sacrum and coccyx. The female pelvis is larger in all diameters than the male. The bones of the lower extremity, which is joined to the pelvis by the head of the thigh bone (the femur), making a ball and socket joint at the acetabulum, are the two bones of the leg, the tibia and fibula; the patella or knee-cap; and the twenty-six bones of the ankle and foot.]

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_.

=THE BRONCHIAL TUBES=

=ORGANS INVOLVED IN FIRST STAGES OF DIGESTION=]

(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.

=LEFT AURICLE AND LEFT VENTRICLE=

The heart, the main pump of the circulatory system, rests on the diaphragm between the two lungs. The heart is enclosed in a smooth, moist membrane or sac, the pericardium, which allows it to dilate and contract without friction against the adjoining parts. There are four cavities in the heart, the right and left auricle, and the right and left ventricle. The auricles, which are thinner walled, collect blood from the veins, while the thicker and stronger walled ventricles force the blood into the arteries. The left auricle pumps the purified blood into the left ventricle, the valve between the auricle and ventricle opening to allow this passage. When the left ventricle is full the valve between its chamber and that of the auricle closes, the ventricle itself contracts down, and the blood is pumped out through the aorta to supply all the tissues of the body.

After leaving the left ventricle through the aorta the purified blood is carried to the head, arms, trunk, and lower limbs, etc. Finally, after being deprived of its oxygen as it passes through the tiny end-arteries, or capillaries, of the tissues it has to nourish, it is collected in the veins and is emptied into the right auricle. Passing from the right auricle to the right ventricle, this impure blood, which is of a dull purplish color, is pumped into the lungs, where it is deprived of its waste gases and once more takes up a fresh supply of oxygen. Bright scarlet in color again, it now is collected and carried to the left auricle by the pulmonary veins. From the auricle it passes through the mitral valve to the left ventricle, whence it is once more pumped out through the aorta to supply the tissues.]

Left: larynx from behind. Middle: cross-section of the pharynx. Right: section through larynx.]

The organs of respiration are the nose, throat, larynx, windpipe or trachea, and the two lungs. On the outer walls of the nasal cavities are three shelves known as the turbinated bones, the surfaces of which contain blood-vessels to heat the air as it passes through the nose. The mucus which constantly forms on the lining membrane of the nose and the little hairs in the nostrils, act as screens, preventing dust being breathed into the lungs. The pharynx is the cavity behind the nose, mouth and larynx. The larynx forms a prominence in the throat known as the “Adam’s Apple.” It contains the vocal cords, the vibrations of which, as air from the lungs passes through them, give rise to voice sounds. The epiglottis is a cartilaginous curtain above the larynx which blocks up its entrance when food is being swallowed. The trachea or windpipe is a continuation of the larynx. Shortly after entering the chest it divides into two main branches, the right and left branches, which lead to all parts of the lungs. The lungs, two spongy, air-filled organs, take up most of the space in the chest-box or thorax. The smallest end-branches of the bronchial tubes open into numerous tiny sacs known as the air vesicles, in the walls of which the end-branches of the capillaries ramify. Here the impure gases in the blood escape through the vessel walls into the air vesicles, while the oxygen breathed into the lungs is taken up the same way by the blood in the vessels.]

=CORD WITH DURA MATER=

=THE ARRANGEMENT OF THE DURA MATER=

The nervous system consists of (1) the brain; (2) the spinal cord; (3) the nerves which run off from these structures; and (4) the sympathetic system. The chief mass of the brain is known as the cerebrum, or fore-brain, the small mass at the lower part being termed the cerebellum, or little brain. From the brain, which is contained within the bony skull, twelve pairs of cranial nerves proceed. The most important of these are the first or nerve of smell, the second (sight), eighth (hearing), and twelfth (taste). The fifth, one of the most important nerves of sensation, has three main branches running to the orbit and forehead, the jaws and teeth, and the skin of the face. Six of the twelve pairs of cranial nerves govern the movements of different parts (motor nerves), others have to do with the special sense organs, taste, smell, hearing, and sight (sensory nerves), and others are a combination of motor and sensory nerves. The spinal cord is a continuation of the brain, and is contained in the hollow canal running through the vertebræ of the spine. From it thirty-one pairs of nerves originate. The nerves which run to the arm are collected in a network called the brachial plexus. In the same way the great nerves to the leg come together in the lumbar plexus. The sympathetic nervous system consists of a main nerve trunk running downward along the spine from the skull to the coccyx. This sympathetic system communicates indirectly with the brain and spinal cord, and also with all the great arteries and other important structures in the abdomen.

The dura mater is the strong external cranial membrane which adheres to the skull and also penetrates into the cavities of the brain, dividing it into partially separate compartments. These dividing portions of the dura mater may be seen at A, A, in the diagram above. B marks the various venous blood sinuses of the brain, which receive blood from veins in the different parts of the brain, and, merging into one large sinus (seen at lower right of diagram), afterwards become the jugular vein. C is the great cerebral vein. The Roman numerals mark the great cranial nerves.]

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_.

The _brain_, which fills the head, consists of two parts: the _Cerebrum_, or greater brain, and the _Cerebellum_, or lesser brain, placed behind and below the larger one. From this brain, nerves run to every muscle of the body, enabling them to move the limbs and body as the mind directs; and another set of nerves run from every part of the body and skin to the brain, enabling the mind to know and feel all that goes on.

The brain is connected with the spinal cord by a flat band of brain matter, that lies on the inside of the occipital bone, called the _Medulla Oblongata_, or the Oblong Marrow. The _spinal cord_ runs through a large hole in the occipital bone and right down the open tube formed by the spinal vertebræ, to the bottom of the backbone, and, all along its course, nerves leave it and enter it, as in the brain.

The _organ of sight_ consists of the _two eyes_, which receive every image that we see, and transmit it to the brain. The _organ of hearing_ consists of the _two ears_, by which we receive all the waves of sound that we hear, and transmit them to the brain. The _organ of smell_ is in the upper part of the _nose_; the _organ of taste_ at the hinder part of the _tongue_.

The _organ of the voice_ is contained in the _larynx_ in the neck, which joins the head to the body. Just under the chin in front of the neck you can feel what is called the _Adam’s Apple_, which is the front of the larynx, or voice-box, by which the air coming out of the lungs is formed into sounds.

The _sounds_ are formed into words by the _mouth_, _tongue_, and _teeth_.

UPPER JAW: 1, 2, incisors; 3, canine; 4, 5, premolars; 6, 7, 8, molars.

LOWER JAW: 1, 2, incisors; 3, canine; 4, 5, premolars; 6, 7, 8, molars.]

THE FIVE GATEWAYS OF KNOWLEDGE

These gateways--which we otherwise name the Organs of the Senses,
and call in our mother speech, the Eye, the Ear, the Nose, the
Mouth, and the Skin--are instruments by which we _see_, and _hear_,
and _smell_, and _taste_, and _touch_: at once loopholes through
which the soul gazes out upon the world, and the world gazes in upon
the soul.

THE EAR: THE MARVELOUS ORGAN OF HEARING

The ear is divided into three parts:

(1) The external ear, made up of the outer portion and passage-way which leads up to the drum.

(2) The middle ear or drum, the continuation of the ear passage internal to the drum membrane, and

(3) The internal ear containing the labyrinth and the nerve of hearing.

DESCRIPTION OF THE EXTERNAL EAR

The outermost part, the skin-covered _auricle_, contains no bone, being simply a mass of cartilage covered by skin. It acts as a sound catcher and improves the hearing by directing sound-waves into the opening or external _meatus_. This meatus or passage-way runs directly inward for an inch and a half. The inner half of the passage-way runs through solid bone, ending abruptly at the membrane or sounding-board of the ear.