Hygiene for beginners

Front matter

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22101438976

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Preface

In 1894 I had the honour of writing a small Primer on Hygiene which was intended for the use of higher-grade school children and for those who attended elementary lectures on Hygiene, as given in Evening Continuation Classes, Mechanics’ Institutions, and University Extension and County Council courses. It is, however, obvious that a knowledge of elementary Anatomy and Physiology is necessary before even the main principles of Hygiene can be understood. I have therefore, in accordance with many requests, considerably enlarged the Primer, and have included a rough outline of Anatomy and Physiology merely as an introduction to the chapters on Hygiene. These chapters have been thoroughly revised, and numerous additions have been made. The book will, I hope, be found to contain all that it is necessary for the general public to know if they wish to escape the ravages of preventible disease.

Thirty of the illustrations have been taken, by kind permission, from Professor Huxley’s Elementary Lessons on Physiology ; the rest are either new or are alterations from old figures.

ERNEST SEPTIMUS REYNOLDS.

Manchester, October 1896.

This reprint has been carefully revised, and certain alterations which our increased knowledge of disease rendered necessary have been made.

ERNEST SEPTIMUS REYNOLDS.

Manchester, December 1901.

A further revision of this book has been made, and the number of “ Questions ” at the end of each chapter has been increased.

ERNEST SEPTIMUS REYNOLDS.

Manchester, October 1905.

Book I Elementary Anatomy And Physiolooy

CHAP. PAOF.

entiation — Life-history of man ..... 1

2. The Skeleton .\nd Connective Tissues. — Cartilage and

Bone — Tlieir compo.sition and structure — Connective Tissue — The Skeleton — Joints ..... 0

3. The Muscular System. — Structure of muscle — Levers —

How muscles act — Standing — Walking .... 23

4. The Nervous System. — The brain — The spinal cord — The

peripheral nerves — Nerve cells and fibres — How the nervous system acts — The sympathetic system . . 28

r». The Blood. — Chemical composition — Coagulation of the blood — The circulation of the blood — The heart and its structure — The distribution of blood to the body — The return of blood from the body to the heart — The portal circulation — The blood-flow to the lungs, and its return -Structure of arteries, capillaries, and veins — Tlie physiology of the circulation— The heart beat — The blood in the vessels — Nervous mechanism of the heart and Mood-vessels — The lymjdiatic system .... 36 viii

CHAP.

6. The Respikatory System. — Structure of uose, pharynx,

larynx, trachea, bronchi, and lungs — Mucous membranes — The thorax and its contents — The physiology of respiration— Inspiration — Expiration — The composition of the atmosphere — Changes in air during combustion and during respiration— Changes in blood during respiration — Arterial and venous blood

7. The DiCxESTive Organs. — The mouth — The tongue— The

teeth and their structure — The abdomen and its contents — The stomach — The intestines — Glands, secretions, and excretions — The salivary glands — The liver — The pancreas .........

8. Food, its Digestion and Assimilation. — Nature of food —

IMilk — Nitrogenous bodies — Fatty constituents — Sugary and starchy constituents — Mineral salts and vegetable acids and salts — Water — The physiology of digestion — The saliva — The gastric juice — The bile — The pancreatic juice — The functions of the liver — Ductless glands — The spleen — The thyroid gland — Conversion of food into work and heat — Animal heat, its production and loss .

9. Excretion.— The kidneys — The bladder — The skin — The

sweat — The hair and nails ......

1. Introduction. — Definition of Hygiene — Short history —

Preventible and non - preventible disease — Causes of disease — Order of book .......

2. Parasites and their Action on the Human Body. —

Definition — Nature — Animal parasites — Vegetable parasites— How germs cause disease — How the body resists the germs

PAGE

CONTENTS

IX

CHAP. PAGE

3. The Impurities of Air, and the Diseases they cause. — ■

Impurities of air — Source of impurities — Self-purificatiou of atmosphere — Standard of purity — Diseases produced by various impurities . ....... 117

4. Water and its Impurities. ^ — Uses of water — Its com-

position— Sources of supply — Storage — Amount required — Character of good drinking water — Hard and soft water — Impurities of water — Diseases from insufficient or impure water — Purification of water . . . .123

5. Food, Cooking, and Beverages. — Proper proportion of

various constituents of food— Study of various foods —

Milk — Flesh of animals — Vegetable foods — Saccharine substances — Condiments— The construction of dietaries — Variety — Arrangement of meals — Adaptation of food to varying circumstances — Feeding of infants — Diet in sickness — -Cooking of animal and vegetable foods — Preservation of food — Diseases due to food — Beverages, as tea, coffee, cocoa, and alcohol — Tobacco . . .134

6. Personal Health. — Hereditary diseases — Personal cleanli-

ness— The skin — Warm water and soap — Cold and hot baths — Hair, teeth, and nails — Exercise and rest — Regularity — Clothing — Materials used for dress — Dress construction — Men’s dress — Women’s dress — Boots and shoes — Night attire — The clothing of infants . . 155

7. The House. — Situation and soil — The construction of the

house — Decoration and furniture — Ventilation — Amount of fresh air required — Objects of ventilation — Natural forces aiding ventilation — Methods of ventilation — Natural ventilation — Artificial ventilation — Warming by fires, stoves, and hot pipes — Artificial lighting — AVater supply of house — House refuse and its disposal — Removal of dry refuse— Disposal of liquid refuse — Sewers — Drains — Traps — Water-closets . . . . . .170

8. Infectious Diseases and their Prevention.— Infectious

and contagious diseases — How germs are conveyed and received — Meaning and course of a fever — Measles —

Scarlet fever — German measles — Chicken-pox — Smallpox

X

CHAP.

— Cowpox and vaccination — Typhoid fever — Typhus fever — Diphtheria — Whooping cough — Mumps — Consumption or phthisis — Children and infectious diseases — Precautions when fever is in a house — Disinfection after fever — Disinfectants, deodorants, and antiseptics .

9. Medical and Surgical Emergencies and Hints on Sick Nursing. — Unconsciousness — Fainting — Hysteria — Epilepsy — Convulsions in children — Apoplexy — Poisoning by acids and alkalies, corrosive sublimate, sugar of lead, phosphorus, bad food, false mushrooms, alcohol, and opium — Emetics — Artificial respiration — Suffocation — Choking — Croup — Foreign bodies in ’eye, nose, and ear — Bleeding fi om nose, lungs, and stomach — External bleeding — Cuts— Bruises — Burns and scalds — Bites and stings — Shock — Concussion — Compression of brain — Sprains — Dislocations — Fractures — Splints — Carrying injured persons — Bandaging — Sick nursing — Poultices — Fomentations — Giving medicines and food

JNDEN ....oei*'*"

PAGE

LIST OF ILLUSTRATIONS

FIG.

1. Amoeba

2. Paramceciiim

3. Hydra

4. Cartilage f). Bone .

6. Section of femur

7. Connective ti.ssue

8. Adipo.se tissue

9. Vertebral column

10. A dorsal vertebra

11. Atlas and axis

12. Side view of skull

13. Thorax, shoulder girdle, and upper extremity

14. Pelvis and lower extremity

15. Elbow-joint

16. Striated muscular fibre

17. Action of biceps on elbow-joint

19. The brain ....

20. Spinal cord

21. Nerve cells and fibres .

22. Red and white blood corpuscles

23. Heart and lungs

24. Pericardium

25. Involuntary muscle cells

PAGF,

4 6 7 9

14 17 19 21

24 26

30 32 37

41 41 xii

FIO. PAOE

2t). Right side of heart ........ 43

27. Left side of heart ........ 44

28. Diagram of blood circulation ...... 46

29. Circulation in frog’s foot ....... 49

30. Arteries and capillaries ....... 52

31. Valves and veins ........ 53

33. Section of mouth, nose, pharynx, and larynx ... 61

34. Diagram of thorax ........ 63

36. Ciliated epithelium ........ 65

37. Mouth and tongue . . . . . . .74

38. Structure of teeth . . . . . . . .75

39. Organs in abdomen ........ 77

41. A stomach gland ........ 80

42. Diagram of wall of small intestine ..... 81

43. Structure of glands ........ 83

44. Salivary glands ......... 84

46. Structure of liver . 86

47. Spleen and pancreas ........ 87

48. Structure of kidney 100

49. Diagram of kidney tubule ....... 101

54. Round worm . . . . . . . . .Ill

55. Thread worm ......... Ill

56. Yeast plant . . . . . . . . .Ill

57. Ringworm fungus in hair . . . . . . .Ill

58. Micrococci from pus . . . . . . . .112

59. Tubercle bacilli in sputum . . . . . .112

LIST OF ILLUSTRATIONS xiii

FIG. PAGE

CL Cholera spirilli ......... 112

62. Opposing action of germs and cells . . . . .115

63. Sources of water supply ....... 124

64. Pollution of well by sewage . . . . . .129

65. Berkefeld filter ......... 132

66. Feeding-bottle for infants ....... 143

67. Skeleton of natural chest ....... 165

68. Skeleton of chest deformed by corsets . . . .165

69. Foot distorted by tight boots, and natural foot . . . 168

70. Healthy site for house . . . . . . .171

71. Unhealthy site for house ....... 171

72. House on old clay pit . . . . . . .172

73. Bad site improved ........ 172

74. Foundations of house ........ 174

76. Air-currents at open door of a room ..... 178

77. Air-currents in sitting-room with open fire .... 179

78. Simple window ventilator . 180

79. Various ventilators for small room . . . . .180

80. Ventilating gas globe . . . . . . .181

81. Teale’s fire grate . . . . . . . .183

82. Gallon’s hre grate with air-currents in room . . .183

83. Ventilating and heating stove ...... 184

84. Outhouse for refuse ........ 188

86. House polluted by pig sty ....... 191

88. Soil ])ipe and its connections ...... 192

89. Bell trap, I)-trap, and mason’s trap ..... 193

90. Various forms of syphon trap . . . . . .194

91. Gully trap

92. House with good sanitary arrangements . . . .195

93. Old-fashioned valve closet 198

94. Wash-out closet

95. Wash-down closet

XIV

FIG.

96. Sim})le arrangement I'or sulphur fumigation

97. Artificial respiration

98. Rope and poles as an ambulance

99. Esmarck’s bandage

100. Sling for arm

PAGE

. 209

. 216 . 221 . 222 , 222

I

BOOK I

AXl) EHYSIOLOGY

CllAPTEE I

Before commencing the study oi‘ Hygiene, which, as will be explained later, is the science which teaches us how to keep the body in health, it is necessary to know something of the body itself ; of what parts it is made up, and the work which each part has to do.

Work, either mental or muscular, is the end and object of the earthly life. Mental work is performed by one part of the body called the nervous system, and muscular work by another part known as the muscular system. As Foster says, “ the master tissues of the body are the muscular and nervous tissues ; all the other tissues may be regarded as the servants of these.” In order that the nervous tissues may be protected from injury, and in order to support and hold together the soft parts of the body, there is provided a firm framework of bone, which is known as the skeleton, and masses of binding fibres known as connective tissue. The nervous and muscular structures cannot perform work out of nothing, but have to be provided with food, which is taken in and prepared by the digestive system so that it can be carried by the blood in the circulatory system to the various parts of the body and there transformed into work. In addition to food, air is required in order that the chemical changes in the body may proceed, and this is taken in by the respiratory system. After the food and air have done their (S- B work, certain waste matters ai'e left, and tliese are got rid of by means of organs forming an excretory system. It will be therefore necessary for ns in e.\aniining the human body to consider the nervous and muscular systems, the skeleton and connective tissues, the digestive, circulatory, respiratory, and excretory systems.

Certain terms and certain elementary facts must be explained before we can proceed.

The study of the various parts Avhich make up the body is known as Anatomy (Gr. ana — up, and tcmno = I cut ; anatome = a dissection), and the study of the work which has to be performed by each of these various parts is known as Physiology (Gr. p/nms = nature, logos = discourse ; pAiisfofogia = an impiiry into the nature of things). To put it in another way, anatomy is the study of the structures which make up the body, and physiology is a study of their functions. Each of the definite parts of the body which differs in both structure and function from the other parts is known as an organ, such as the heart or the stomach. If any organ is examined carefully by the aid of a microscope it will be found to consist of parts which differ one from another, and these various parts making up an organ are known as tissues.

If now we were to examine the tissues of the body chemically, we should find that they were made up of but a few of the numerous elementary substances known to the chemist ; we should in fact only find the gases oxygen, hydrogen, nitrogen, clilorine, and fluorine, the non-metallic solids carbon, sulphur, and phosphorus, aird the metals sodium, potassium, calcium, magnesium, and iron. These elements are not found in tlie body in the free state, but are combined in various ways one with another, forming more or less complicated substances. The whole body has originated from a single minute jelly-like structure, consisting chemically of a complicated material known as protoplasm, and the adult body is made up of many compounds derived more or less directly from this. These bodies are, chemically speaking, generally very complex, but sometimes are simjde in constitution, as common salt or hydrochloric acid.

There exists in fresh -water ponds a very minute animal known by the name of the amoeba. Tliis is a little particle of almost clear jelly of irregular shape, often having a darker part

CHAP. I in the centre, known as the nnclens. Such a structure is composed wholly of protoplasm, and is known anatomically as a cell. If watched under the microscope for some time it will be seen to gradually change its shape and to move its position ; it will slowly surround and lake into its substance small particles ol food lying near it, and after a time it will cast out the waste matter left after it has extracted all the nourishment from the

Fig. 1. — The Amoeba, showing irregular shape, processes, nucleus, and food particles (a), the amoeba dividing (6), with the two re, suiting anicebic (c). x x .1

food particle. The amoeba is in fact a minute animal, living an independent existence, able to move, to feed, and to grow. After the animal has reached a certain size, the nucleus may be seen to divide into two ; then the whole body of the animal divides into two, one mass surrounding each nucleu.s, and in this way two separate amoebse are formed, so alike as to be indistinguishable one from the other (Fig. 1).

A little higher in the scale of animal life we find cells living an independent existence, but, unlike the amoebse, the shape remaining constant ; they can move rapidly from place to place by means of multitudes of tine hair-like processes from the surface, called cilia, which, acting like oars, are able to propel the animal in various directions ; food is taken by such ciliated cells through a small opening in the cell, leading into a channel or cavity (Fig. 2). Still more advanced are animals not composed of single cells, but of many cells very similar to each other clustered together to form a kind of colony ; sometimes, as in the case of the sponge, a framework is thrown off from the cells, and this holds the compound animal together.

Then we find animals made up of aggregations of cells which

^ Tlie.se .signs will be used when the figure is a much magnified illu.stration of the subject.

iiHficiuni, showing cilia, nucleus, and opening into cell for food jtarticles.

X X.

differ slightly in structure, and this is found to he due to the fact that hy a division of labour certain of the cells are doing one part of the work necessary for existence, such as preparing food for use, while other cells are entirely occupied in movement. Such a condition occurs in the fresh -water Hydra (Fig. 3), which is a minute animal composed of very numerous cells ; it can attach itself to an object by its base, and at the • free end has several arm-like feelers (tentacles) by means of which it can entangle its prey. It is hollow in the centre, the

cavity being lined by cells which digest its food. The cells on the external surface are of various kinds ; some are for the protection of the surface, others are prolonged into fine muscular fibres running in the body-wall, a third variety are stinging cells which when irritated throw out a long sting and probably paralyse minute animals approaching the hydra, and lastly, certain cells are probably nervous in nature. In a slightly more advanced animal, the jelly-fish, certain groups of cells containing pigment are arranged so as to form primitive eyes.

And this process of difl’erentiation of cells into various shapes and for various purposes goes on as animals liecome more and more highly organised, until in man we have the most complicated and most organised animal.

But just as we have shown that the lowest animals consist of a single cell, and that animals become more advanced the more their cells are differentiated, so in the life-history of man the same process goes on. For each human being commenced life 'as a single round nucleated cell about inch in diameter, consisting of a mass of jirotoplasm with a nucleus. When fertilised this cell rapidly divides into many similar cells which

Fio. 3. — The Hydra (semi-diagramiiiatic), .showing tentacles, body cavity, and externaland internal layers of cells, x X.

CHAT, r by degrees arrange themselves into definite positions and take on different shapes in each position, so as to form definite organs. A special set of cells goes t<j form the brain, another set the muscles, a third set the eye, a fourth the skin, and so on for all the organs of the body.

It is necessary that these various tissues and organs should be held together and supported in order to form the body ; for this purpose a large number of cells are used up in the construction of what are called the connective tissues, which we Avill now study in detail.

t^iUEHTIONS

1. Define “anatomy,” “physiology,” “organ,” “tissue.”

2. What eheniical elements are Ibund in the human body ?

3. Describe an “amoeba,” and a “hydra.”

CHAPTEll II

THE SKELETON AND CONNECTIVE TISSUES

Cartilage and Bone. — In describing the structures whicli support and bold together the various organs of the body, we will first consider the skeleton. In early life this consists almost entirely of cartilage or gristle, a Avldte substance which, in the adult, we find at the ends of all long bones, and which is familiar to every one, as it occurs at the ends of the leg-bone of a chicken or a rabbit. It is bluish-white in colour, and very elastic, so that after being bent it returns to its original shape ;

Fig. 4. — Cartilage showing nucleated cells in lij aline iiiatri.K. x x.

it can moreover be easily cut with a knife. It is made up of a special form of cells enclosed in a bed or matri.v of glassy-like (hyaline) substance containing no blood-vessels (Fig. 4). This

CHA1^ II matrix contains cliemically aEout three-fifths of its v/eight of water, and a body which when boiled forms a complex snlistance known as chondrin. In adult life the great bulk of the cartilage forming the original skeleton has disappeared, having been replaced by bone, but a certain fpiantity still remains covering the ends of the majority of the bones, forming the framework of the windpipe, part of the framework of the nose, and certain ])ortions connecting the ribs to the breast-bone.

This process of transformation of soft cartilage into hard bone commences just before birth, and proceeds rapidly during the early years of life.

Shortly stated, the change is effected by numerouslilood- vessels and siiecial cells growing into the matrix of the cartilage, the cartilage cells breaking up and being absorbed. The bone cells, whicli have many fine processes, arrange themselves in circles around the minute blood-vessels, and throw out a deposit of hard bony substance consisting of mineral and animal matter, leaving spaces or canals for the blood-vessels, these being known as the Haversian canals. In fact, as in cartilage we have cartilage cells embedded

in a matrix, so in bone we have cells embedded in a matrix ; the difference being that in bone there are numerous blood-vessels, and the matrix is firm from the presence of mineral salts (Fig. 5). Suppose we take two similar leg-bones of a rabbit and place

Pio. 5.— Section of compact bone, showing bone cells arrangcil concentrically round the llaversian canals which contain the blood-vessels. X X .

ELEMENTARY ANATOMY ;\ND PHYSIOLOGY hook i one of tliein in a red fire. It will burn away leaving nothing hut a white ash; if this is carefully removed it will be found to be of the same shape as that of the bone, but only about two-thirds of the original weight, and so brittle that it can be crushed to powder in the fingers. The organic or animal matter has been burnt away, and the mineral ash, chiefly composed of phosphate and carbonate of lime, is left. If we now put the other bone in weak hydrochloric acid for some time, the earthy or mineral matter will be dissolved and nothing but the animal matter, again retaining the original shajie of the bone, will be left. If dried it will be found to weigh one-third only of the original bone, and instead of being firm and resistant it can readily be bent in any direction, but being elastic Avill return to the original position when the force is relaxed. This animal matter consists of a substance from which gelatin may be prepared by boiling it with Avater for several hours. It can be seen from these two experiments how intimately mingled are the animal and the earthy matter of bone.

Having now seen what a bone is like both microscopically and chemicall}'-, let us take, say, the thigh-bone of an animal and saw it into two similar halves from toj) to bottom (Fig. 6). We shall find that it consists of two ends and a shaft, the latter being hollow, and the bone surrounding it being dense or compact bone. The ends, on the contrary, are formed of a network of l)one plates enclosing minute cavities making up what is known as cancellous bone tissue. The hollowor medullary cavity in the centre of the shaft is filled up during life with a yellowish material, the yellow marrow, consisting of connective tissue, much fat, and blood-vessels. The sjiaces in the ends of the bone are filled with red marrow which does not contain so much fat, is more fluid, and contains much more blood. The ends of such a long bone are covered with a layer of cartilage. It will further be found that on the outside of the fresh bone (but not covering the cartilaginous ends) there is a sheet or membrane of tissue which can be stripped off. This is called the periosteum, and consists of white fibrous tissue (see below) carrying blood-vessels which supply the 1)one with blood by penetrating into the minute Haversian canals which open on the bone surface. The marrow is supplied by a special blood-vessel which enters the

SKELETON AND CONNEC'I'IVE TISSUES hollow by a conuDaratively large passage, visible to the naked eye, which perforates the shaft.

Connective Tissue. — This is the tissue which, found in all j.arts of the body, helps to join bone to bone and .soft parts

TO to soft p<arts, not only holding organs in their place, but also binding together the various special tissues making up the various organs. Like all other parts of the body, it consisted

originally of cells only, but most of these have been transformed into long threadlike fibres, so that if connective tissue be examined microscopically (Fig. 7) it is seen to consist of tine wavy fibres either passing in all directions, so forming a network, or being arranged side by side ; amongst these white fibres may be found a few yellow branching elastic fibres. In the .spaces called connective tissue spaces there is a fluid containing a few cells, and on the bundles of fibres other cells are attached. Connective tissue may be arranged in a distinct sheet covering a bone (see above) or enclosing muscles or organs like a sheet of paper wrapping up a parcel. At other times it is formed into strong firm bands called tendons, which connect muscular fibres to bones ; or again, strong bands of connective tissue may connect bone to bone, such a band being called a ligament.

Connective ti.«sue is occasionally mixed with carti-

Fio. 7. — Connective fcissne.

a, fibre.s -wiUi cells on them ; h, free cells in spaces ; c, yellow elastic fibre ; d, blooil capillary, xx.

-Adiposc tissue, with cells containing nmch fat. XX.

lage in the tissue known as fibro-cartilage, such as is found between the bodies of the vertebrae and between the pubic bones. Or yellow elastic tissue may be mixed with cartilage in yellow elastic cartilage, present in the external ear framework.

CllAl*. 11

I I

If tlie cells in the connective tissue are tilled with large transparent masses of fat we get adipose tissue (Fig. 8), especially present under the skin of fat people.

The Skeleton

If we contemplate for a moment the human body we shall notice that it consists of several distinct parts ; these are the head (including the face), the trunk (including the upper part, the chest, and the lower part, the abdomen), and the limbs (two arms and two legs). It will further be observed that the mainstay or prop of the whole body is the backbone or spinal column (Fig. 9), on which the head rests, to which the limbs are directly or indirectly attached, and which forms the back part of the chest and abdomen. The spine is also known as the vertebral column.

Pig. 9. — The vertebral colinmi.

A, side view, left side ; B, back ^-iuw; C 1-17, cervical vertebra; ; 1) 1-12, dorsal vertebrie ; L 1-5, lumbar vertebra? ; S, sacrum ; C, coccyx ; sp, spinous processes ; tr, transverse processes.

and it examined in the dried skeleton is found to consist not of one, but of many small bones — the separate vertebrae, more or less similar in shape — resting one on another. The whole column is divided into several regions ; the neck or cervical region, made up of seven vertebrae ; the back projier, or dorsal region, of twelve vertebra) ; the loin or lumbar region, of five vertebriB ; and finally the sacrum, a large curved bone, and the coccyx, a small irregular bone — a grand total of twenty-six bones. Let us examine one vertebra, say the sixth dorsal (Fig. 10), and we shall find that the front part is a solid mass, round in outline, but flat at the top and bottom, being, in fact, like a thick slice cut from the middle of a rod. This front mass is

Fig. 10. — A dorsal vertebra.

A, side view, right side ; B, view from above ; h, body ; tr, transverse processes ;

.'•p, si)inous ])rocess ; ar, jdace on the arch for articulation witli vertebra above ;

11, place on body for articulation of end of rib ; n, canal for spinal cord.

known as the body of the vertebra. From the posterior part of the body there .springs an arch leaving a central hole ; at the back of the arch is a spinous proces.s, and at each side a transverse process. Each of the cervical, dorsal, and lumbar vertebne, with two exce})tion.s, is built up on this jilan • the cervical vertebne are, however, more slightlv constructed, and each transverse process is ])erforated by a small hole, through which an artery goes to the brain ; the lumbar vertebra) are much stronger in every way than tbe dorsal, the bodies, transverse proce.s.ses, and s])inous j)rocesses being heavier and thicker. All the dorsal vertebra) have on their sides and at the tips of the transverse proce.sses small smooth surfaces, to which, as we shall see later, the ribs are attached. The first two cervical vertebne are peculiar, inasmuch as the first consists of a mere oval ring of bone with no body in i'roiit, but with two large hollow kidney-shaped surfaces on the upper sides of the ring, on which surfaces the head rests. The first cervical vertebra for this reason is called the atlas (Fig. 11), from tlie god Atlas, who was sup230sed to hold the world on liis shoulders. The second vertelira would be similar in form to the rest of the cervical vertebrae, except that arising from the upper part of its body is a hard, bony, tooth -like (odontoid) process. If the atlas is placed in position on the top of the second vertebra it will lie seen that the odontoid process exactly fits into the place where the body of the atlas should be ; this process is in reality the body of the atlas, which is displaced and fixed to the body of