Elements of physiology; being an account of the laws and principles of the animal economy, especially in reference to the constitution of man

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Preface

A KNOWLEDGE of the structure of the human body cannot but be considered by every cultivated, intelligent, and inquiring mind, as a most desirable acquisition. In tracing the many curious contrivances which are exhibited in its organization, in perceiving the admirable adaptation of its parts to the performance of their varied offices, and in viewing the whole series of its organs in their mutual relation and subserviency, one exercises the highest faculties of his mind, and acquires information that may be useful in life. Indeed, so obvious is the importance of an acquaintance with the mechanism of our bodily frame, that one, viewing the subject in a general sense, might naturally wonder why Anatomy and Physiology are not considered as indispensable elements of education.

The object of the present work is to give such an account of the structure of the animal body, and

IV PREFACE.

especially of that of man, as well as of the manner in which the various parts of the machineryoperate, as may be readily understood by those who may not previously have directed their attention to investigations of this kind. Science is enriched with several works of great merit on these subjects ; but they either are exclusively intended to exhibit a minute and detailed description of the organization, in order to adapt them to the use of persons who, from their profession, necessarily require an intimate knowledge of the size, proportion, and relative situation of the different parts of the body ; or else they treat of the ftmctions in such a manner as can only be properly understood by those who have previously obtained considerable acquaintance with the structure. The descriptions, moreover, although sufficiently clear and explicit to those who are familiar with such subjects, are generally loaded with technicalities, and the allusions and illustrations, though readily understood and appreciated by the initiated, are but little adapted to interest or instruct the general inquirer.

Nothing so much distinguishes the present age as the eager desire evinced by all classes of society for acquiring scientific knowledge : the crowds attending public lectures, the number and character of the works on various departments of science that

PREFACE. V

daily issue from the press, and even the tone of general conversation, sufficiently shew how anxiously information of this kind is sought after. It has been from the conviction that a work like the present is needed, and not from any belief that I am especially qualified for the task, that I have been induced to undertake it. I have, however, endeavoured to the utmost of my power to fulfil the objects in view, to afford such a description of the various structures of the body as may serve to convey a correct idea of their organization, and to give such an account of their mode of action as appears best to accord with experience and observation.

The professional reader will readily perceive that the descriptions are drawn directlyfrom the objects described. Indeed, that I might do justice to the subject, this was the only method that was left me, in attempting to give to the general reader an account of the intricate construction of many parts of the animal machinery. It was impossible to refer to the various sources of information respecting the uses and applications of the different parts; since, though many of the discoverers of physiological truths be well known, appreciated, and justly venerated by the professional student, still their authority and names can have but little comparative interest or weight with those whose attention is less directed to such inquiries. Neither

VI PREFACE.

has it been deemed necessary to cite the different views taken as to the use and modes of action of the various organs, nor particularly to insist upon the reason why the opinion adopted has been preferred.

Were mankind a little better informed than they generally are of the constitution of their own bodies, and knew how fearftdly and wonderfully they are made, they would be more careftd in avoiding causes that tend to disturb and derange the fimetions; that induce painful and incurable maladies ; that contribute to shorten the limited period of human life : and we should have fewer miserable and deluded dupes of ignorant pretension and impudent quackery.

Introduction

General Observations — Classification of Functions'-Conseryative

Functions — Circulation of the Blood — Respiration — Digestion — ^Nature and Constitution of the Blood — Absorption — Secretion — Functions of Relation — ^Nervous System — ^The External Senses — Foetal Life — Concluding Remarks xt^zxIt

CHAPTER I.— Circulation

General View of Circulation — Opinion of Hippocrates — Theory of Hairey — Discovery of the Absorbents — Structure of the Heart — Condition at the point of death — Structure and Action of the Arteries — Of the Capillaries — Of the Veins — Operation of Transfusion — Heart an involuntary Organ — Heart insensible — ^Effects of the Passions of the Mind — Size of the Heart in proportion to- the other Organs — Mechanical conditions of the Blood Vessels — Circulation influenced by Respiration — ^through the Brain — in the Abdomen 1—43

VllI CONTENTS.

CHAPTER II.— Respiration

Organs of Inspiration — Expiration — Passages through the Diaphragm— Incidental Respiration — Respiration in Birds — in Reptiles — Opinions of the Ancients as to the use of Respiration — Atmosphere — Its Height — Weight — Humidity — ^Temperature— Composition — Changes produced on the Air hy breathing — Quantity of Water thrown off in the Breath — Diminution of Oxygen — Increase of Carbonic Acid — State of Nitrogen — Changes upon the Blood — In Colour — Density — Chemical Constitution — Temperature and Animal Heat — Source and Distribution of — How regulated when the Body is exposed to High and to Low Temperatures — Progressive Development of Animal Heat in the New-bom — Adaptation to the Temperature of different Climates — Hybernation — Voice and Speech - - Respiration of different Gases — Asphyxia — ^Means for restoring the Functions in Suspended Animation 44^115

CHAPTER III.— Digestion

A General Account of the Changes which the food undergoes in the Digestive Organs — Man a Cooking Animal — Food assimilated to the Temperature of the Body in the Mouth— Teeth^ their Structure and Use in various Animate — The Teeth of Man, their Form, Number, and Structure — ^Why there are two Sets — Motions of the Jaw — Saliva, Composition and Use of — Deglutition — General View of the Alimentary Canal — Stomach — ^Duodenum — Small Intestine-— Large Intestine — Liver — Spleen — Pancrea8-~Organ8 of Digestion in Carnivorous Animals— ^in Ruminants*~in Birds — Digestive Apparatus of Man adapted to a greater variety of Food than that of any other Animal — Animal Food, and its proximate principles — Vegetable Food, and its proximate principles — ^One or other most suitable to different climates — Concentration, Variety, Consistence, and Quantity influence the Digestibility of Food —

CONTENTS. IX

Condiments, Salt, Acids, Bitters, Astringents, Aromalics — Hunger and Thirst — Chymification — Gastric Juice — Its peculiar powers — ^Chylification — ^Biliary, Pancreatic, and Intestinal Secretions — Chyle absorbed, and conveyed through intricate channels, becomes gradually assimilated to, and conTerted into perfect Blood — Last efforts for the Abstraction of Nourishment — Drinks — Several substances introduced into the Circulation from the Alimentary Canal without being changed . . 116—185

CHAPTER IV.— The Blood

Blood — Physical Properties of — Colour — The Red Globules — Their Form and Constitution — Smaller and more numerous in Mammalia — Odoui^Characteristic of the Animal to which it belongs — Consistence — Temperature — Specific Gravity— Quantity of in the Body — Coagulation — ^Relative Proportion of Serum and Clot — Serum — Fibrin — Oil of the Blood — ^Table of Analysis of— Vital Properties 186-201

CHAPTER v.— Absorption

Purposes served by the function of Absorption — ^Absorption from the Skin — From Mucous Membranes — From Serous Membranes— From Cellular Tissue — From the Surfaces of the Joints — ^Interstitial Absorption — Its importance in carrying off the old worn-out particles, and consequent subservience to the renewal of the different parts of the body — Special Organs of Absorption — Discovery of — Controversies respecting — Lacteals and Lymphatics — ^Their excessive number — Lymphatic Glands — ^Their Office — Case of puncture from Dissection — Endosmose and Exosmose — Venous Absorption — Causes influencing Absorption — Causes which tend to increase or diminish the risk from exposure to contagious Diseases 202—232

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CONTENTS.

CHAPTER VI.— Sechbtiow

Preliminary Obtenrations — ClaMification of Secretions — Matter of Perspiration — Scarf-skin seryes as a barrier between the Body and the External World — ^The vast extent of the two general Mucous Membranes — Only one Mucous Membrane in Animals below the class of Mammalia — Gaseous Exhalations — Follicular Secretions — Unctuous Secretion of the Skin — Necessity of Personal Cleanliness — liquor of the Eyelids — Wax of the Ears — ^Musk, and other Odorous Secretions of Animals — Glandular Secretions — Arrangement of the Glands — Tears — ^Effects of the passions and emotions of the Mind upon Lachrymal Glands — Why Women and Children shed Tears easily — Secretions connected with Digestion adyerted to — Structure and Use of the Kidneys — ^The very compound nature of the Urine — Urine carries off the superfluous, useless, and worn-out particles from the System — The quantity of Urine regulates the balance of Fluids in the Body — Sugar in the Urine — Urinary Concretions — Urinary Bladder — its Structure and Use — Partly under the Control of the Will — Glandular Bodies, whose use has not been ascertained — Interstitial Secretion— Nutrition, Growth, and Renewal of the yarious Textures of the Body. .....* 233—264

CHAPTER VII.— Nervous System

Introductory Remarks — Hairy Scalp— Skull formed of separate Bones — Advantages of this Construction — Consists oif two Plates — Advantages of — Membranes of the Brain, and the Purposes they serve — Divisions of the Brain — Presents one Continuous Surface, without the slightest trace of Division — Dr Spurzheim's Demonstration of — Enormous Quantity of Water collected in — Microscopic Observations of Bauer — Of Ehrenberg — Structure described — Evolution of the Nervous System in site and complexity accompanied with Parallel

CONTENTS. Zl

Advances in the Higher Instincts and Sagacity — Development of the Brain in the Foetus keeps pace with that of the System in general — ^Weight of the Brain in proportion to that of the Body — Size in proportion to the rest of the Nervous System — Brain the Seat of the Mind — Results of Experiments on — Spinal Marrow, its Structure and Developments-Views and Experiments of Sir Charles Bell — Classification of the Nerves^ Nerves of the Specific Senses — ^Announce the properties of External Bodies — Motiferous Nerves — Convey the Commands of the Will — Respiratory Nerves — Indicate the Instinctive Feelings, Passions, and Emotions of the Mind — ^Their Universal Distribution — Regular Double-rooted Nerves — One Root transmits the Mandates of the Will — ^The other communicates Impressions received — Ganglionic Nerves — Immediate Seat of Individual Vitality of the different Organs of the Body — Their General Connexions — Universal Distribution — Four great Ganglionic Nervous Centres 265—339

CHAPTER VIII.— Sight

Arrangement of the different parts of the Apparatus of Sight — Appendages of the Eye — The Orbit — The Eyebrows — The Eyelashes — ^The Eyelids and their Motions — Lachrymal Apparatus— ^Motions of the Eyeball — ^The Globe of the Eye capable of Motion in every direction — ^The Muscles by which the Movements of the Eye are effected, as under the command of the Will, and by Instinctive Feelings — How we see an object smgle with two Eyes — Regulation of the Sphere of Vision — Compound Eyes of Insects — Some species of Butterflies furnished with 34,650 Eyes — Squinting — Various Causes of— The Globe of the Eye — Sclerotic Coat gives protection, and affords insertion to other parts — Choroid Coat — Furnished with a Dark Secretion to absorb Light — Its intimate Connexion with the Retina— The Iris, or Variegated Curtain — ^The Hole in its centre, the Pupil — Regulates the quantity of Light admitted in the Posterior Chamber — A single object held close to one Eye, several Images produced, and the object appears multimm

• •

XU COXTENTO.

• plied — ^Transparent parts of the Eye — Aqueous Hamoar very

rapidly renewed — Adaptation of the Eye to near and distant, to large and minute objects — Crystalline Lens — ^Its beautifol Organization — ^Vitreous Humonr — ^The Retina the immediate Organ of Sight — ^Manner in which the Retina may see its own Blood-Yessels — Insensibility to light at the entrance of the Optic Nerve— Seat of distinct Vision — Curious effects from indirect Vision — Continuance of the Impression of Light- Cause of the appearance of Light when the eye is struck — ^Refraction of Light — Short-sightedness — Long-sightedness — Sun-beam decomposed into seren coloured rayfr — ^Means by which we estimate the size and distance of objects, by the Visual Angle, the Intensity of Light, Shade, and Colour, and by contrast with other known objects 340—393

CHAPTER IX.— Hearing

Of the Nature of Sound— .Grave and Acute Tones— Number of Vibrations appreciable by the Human Ear— Transmission of Sounds— Velocity of Sound — Stethoscope— Echo— External Ear adapted for collecting Vibrations — Middle Ear or Drum constructed for the Transmission and Modification of the Vibrations^Different Apparatus of— Internal Ear or Labyrinth the immediate seat of the Sense of Hearing— Construction and Apparatus of— General Inferences deduced from the Examination of the Structure as a whole 399—421

CHAPTER X.— Touch

General Observations on Touch — Its universal diffusion over the surface of the Body — External Integuments — ^The Scarf-skin, forming the barrier between the living and the dead-.-The Mucous Web the especial seat of Colour— Albinos — Remarkable case of a dark Hindoo becoming fair— True skin, that of which leather is made— Its External Surface the immediate seat of the Sense of Touch— iTact and Touch— All parts not equally

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CONTENTS. Xin

susceptible to the impressions of Touclu^Iiifonns us of the condition and properties of External Objects— ^The most important Guardian of the Body— Less liable to be imposed upon, and to bear false witness, than the other Senses— The confidence placed in it— The superiority enjoyed by Man in the ezceUency of this Sense— Case of J. Mitchell, bom Blind and Deaf 422-437

CHAPTER XI.— Smell and Taste

Intimate connexion between Smell and Taste— Not of much importance as Intellectual Channel8.«—SMBLLH-«The Nostrils- Confidence reposed in Smell by several of the Lower Animals Its excellence in the Dog— Smell in Vultures — In the Rayen- In Fishes— i^Odours— ^Gratification derived from Odours influenced by Constitution^ Habit, &c. — Classification of-«Permanence» Extent, and Divisibility of-— Morbid Conditions — ^Taste. —Seat of — PapiUse of the Tongue— Savours — Classification of — Influence of Habit — Acquired Tastes— Affected by the State of the Stomach — Morbid Conditions— Gustatory Organs in different Classes of Annals— The Condition of Matter necessary to excite Taste 438-463

CHAPTER XII.— Motion

Organs of Motion consist of the Passive and the Active— Bones — ^Their textures and various Forms— Their Chemical constitution-^Adaptation to the purposes they subserve— Variety of Connexion— Gristle— Its peculiar Organization— Its great elasticity—Forms the Principal Springs of the Animal Machine- Subservient to Mechanical Movements— Elastic Cushions — Ligament— Its Structure-— A very Common Tissue in Animal Bodies-^Presents great varieties, and subservient to many purposes—Elastic Ligamentous Tissue a substitute for Muscular Power-^Continues its Action in the Dead Body— Tendon- Varieties in the Form of— Bears concentrated Muscular Force

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Xir CONTENTS.

— ^Tnmsfen Musonkr Power— MuBcular Fibre— .Characteristic Property VitaL—Organizatioii— Chemical Constitution — Muscular Action-^Changes in the State of Action and Repose- Exciting causes of Muscular Action— The Will— Instinct and Sympathy— luToluntary Muscular Motion— Influence of Disease—Mechanical and Chemical Excitants— Remarkable Effects of Galvanism on the Body of an Executed Criminal— Various Modifications of the Actions of Muscles in the Preservation of the Attitudes, and in Performance of Motion— Force of Muscles —How modified. ■ Musnilnr Vigour in Different Races- Duration of Action— Velocity of Motion— In Man — In Animals^-Mutual adaptation of Structure and Function in Animal Bodies 4 64-4 94

CHAPTER XIII.— F(ETAL Lipe

General Observations— Progress of the formation of the Egg in the Common Hen— The Molecule — All the other parts subservient to it— Incubation — Formation of the Chick in the different stages — ^Membranes surrounding it in the egg — ^Table of periods of Gestation in several Mammalia — The Vesicle— -Its Passage — ^Arrival in the Uterus — Changes it undergoes through the various periods of Gestation, and the Functions successively called into Action — Respiration in the Foetus — Regulation of Temperature — Secretions poured into the Alimentary Canal — Circulation of the Blood of the Foetus — ^Milk—Principal Constituents of — Proportion of these in diffu^nt Animals — Conclusion ' 495—514

INTRODUCTION.

General Obteiratioiu— ChuBification of Fuiictioii»— ConiervatiTe Functiona Circulatioa of the Blood— Respintioa—DigeBtion— Nature and Conititutianof the Blood— Absorption— Secretion— Functions of Rdation— Nervous System— Extonal Senses— Foetal Life— Concluding Remarks.

The material world around us comprises two great divisions— ^the organic and inorganic kingdoms of nature. The latter consists of bodies whose elements are influenced by the laws of attraction, repulsion, gravity, electricity, and other powers, the investigation of which constitutes the provinces of the chemist and natural philosopher. Organic bodies, on the other hand, are endowed with certain powers, in virtue of which they are enabled to resist the influences to which mere dead matter is subject, and to a certain extent to modify and control the properties of matter, so as to render them subservient to their own preservation and development. These controlling powers, laws, or properties^ as they have been termed, are called vital, and enable living bodies to resist the mechanical and chemical tendencies of the materials of their composition that, left to themselves, would subvert and destroy the necessary arrangement of their organization.

The living organized kingdom of nature comprehends two grand divisions, the animal and the vegetable ; and although at the first glance there seems nothing in common between lordly man and the humble zoophyte, scarcely distinguishable from the rock on which it is fixed, or the simple lichen that clothes the aged tree, yet, on a more close and patient examination, we shall find them per-

XVI INTRODUCTION.

forming functions in seyeral respects analogous to each other.

The organs and functions of living bodies may be arranged under the four following heads: — First, Those that contribute to the support and preservation of the individual, which may be termed the Conservative. Secondly, Those whereby living bodies become affected by the external objects around them; namely, of appropriate instruments, the organs of sense, by means of which they are enabled to take cognizance of the impressions received, and the agents of locomotion, comprising together what have been called the Organs of Relation. By a third set of organs, the most effectual measures are provided for the permanent continuation of the race. Lastly, man is possessed of faculties that enable him to trace effects to their causes, to distinguish between virtue and vice, to reflect upon events that have passed, to anticipate the issues of the future ; and, above all, to raise his mind to the Supreme Intelligence, the Cause of causes, to whom all nature owes her existence, and to whom, with more or less clearness of conviction, he feels conscious of responsibility.

On the present occasion our attention will be exclusively directed to the consideration of the first two classes of functions, and the machinery engaged in their performance, namely, the conservative, and those of relation.

In the first place, we shall examine into the distribution of the fluids through the different parts of the system, or the Circulation of the Blood.

In considering this function, and the apparatus by which it is exercised, we shall find in man, and in those animals most closely allied to him in their organization, that the heart is one of the most efficient agents for this purpose ; that it forms, as it were, the fountain-head from which issue forth the vital streams to distribute themselves throughout the whole body, and to which they are again returned. We shall find that by the action of one of its cavities the blood is propelled into a large tube opening

INTBODUCMON. XVU

into it ; that this tube, by its divisions and subdivisions, conveys the blood to every organ and every tissue, in the requisite quantity, and with the due degree of force ; that part of the blood is deposited to effect growth and renewal of their textures, part separated in the form of secretions necessary for different purposes, and a third portion thrown off as superfluous or deleterious, thereby purifying the body.

Having been subservient to these and various other functions in the system, the blood will be perceived to have undergone an alteration in appearance and properties : from a bright vermilion hue it becomes changed to a dark purple, and is rendered inadequate to the due performance of the purposes it subserves. It is therefore returned from all parts of the system by another set of vessels, that form reiterated unions with each other, and ultimately terminate by three trunks in another cavity of the heart. Thus, we have two currents of blood in opposite directions, the one proceeding from the heart to every part of the system, the other from all parts of the system towards the heart.

In the next place, by the action of the heart it is forced through the innumerable ramifications of an appropriate tube through the minute tissue of the lungs, where, from the influence of the atmospheric air, and by the extrication of noxious vapours, it becomes purified, and again changed in colour and properties from the dark purple to the vermilion red. Being thus once more prepared for the various uses to which it is applied, it is conveyed to the heart to be propelled to the system.

Such is the incessant course of the blood through the body, from the commencement of life till its termination.

Respiration is the next conservative function to which we shall direct our attention. It is in a great measure subservient to circulation, its chief final purpose being to perfect the blood, to afford an opportunity for the escape of noxious vapours from it, and to impart a portion of atmospheric air necessary to its healthy constitution.

XYIU INTRODUOTIOIf.

The lungs, the organs directly suhservient to this function, are placed without the cavity of the chest. They are of a light and spongy texture, and consist principally of the ramifications of blood-vessels, along with numberless air-tubes that terminate in minute cells. By the alternate enlargement and diminution of the chest, the air in these cells is constantly renewed, receiving from the blood those vapours that are to be carried o£f by the breath, and imparting to it those elements of its constitution that may be required. The chemical changes that the air sufieis in breathing, and the alterations the blood undergoes by exposure to it in the lungs, enable us to appreciate the effects that take place; while the alteration produced upon the blood in the lungs, and the converse change occurring in the system, furnish an explanation of the curious and interesting phenomena connected with tiie production and regulation of animal temperature.

In the alternate movements that take place in breathing, various interesting muscular actions are called into play, and numerous secondary effects result from the exercise of this important function. Among these the conversion of air into Sound and Ariiculate Speech is not the least curious in the contrivances by which it is effected. At the upper part of the windpipe is placed the apparatus of voice — an apparatus, as we shall find, constructed upon the principles both of the wind and of the stringed instrument, while by the management of the tongue, lips, and other parts, the voice is converted into articulate language.

Our attention will next be directed to the function of IHgeHion^ by which food is converted into blood, in order to compensate for the constant expenditure that takes place. Here we shall trace the progress of the food, and the various changes to which it is subjected, from its fimt* introduction into the mouth till it be converted into arterial blood.

In thefiist place, we find that in the mouth it is>ve» duced by the action of the teeth to a minute state of me-

IlfTRODUCnON. ZIJC

ohsnical divieion, thoroughly intennized and oombined with the sahTary secretions.

It is then transferred to the stomach, where it meets with a peculiar secretion termed the gastric juice, and wh^« it remains for some time, becoming converted into a pultaceous mass named chyme. From the stomach the chyme passes into the intestinal canal, where it is joined by several fluids, such as the bile and other juices, and where a nutritious fluid capable of being received into the system is formed, named chyle.

The chyle is drunk up from the intestinal canal by numerous minute tubes, which convey it through certain bodies, termed lymphatic glands, and afterwards pour it into the veins passing to the heart, in which it becomes mingled with the general mass of blood ; and after transmission to the Inngs, and exposure to the air, its conversion into arterial blood is completed. Drinks, which undergo no change or decomposition, are introduced in a more direct manner. They are immediately absorbed by the veins, and thus enter at once the general mass of circulating fluids. Various other materials, such as colouring matter, odorous principles, and chemical substances, that resist the influence of the digestive apparatus, are likewise taken up by veins, and carried through the liver, so that while they are filtered through that organ, an opportunity is afforded for their partly being cast out along with the secretion of bile. At all events, they here become subject to intermixture with the blood, and undergo modifications before their introduction into the system at large.

Having taken under consideration the means by which the Blood is circulated through the body, the alterations it is subjected to, the manner of its purification, and the nfode of its formation and renewal, we shall be prepared to Miter upon the examination of its constitution. As might be anticipated, we shall find it a very peculiar and. compound fluid, containing, if not all the prineipleay at least all the elements that go to the formation of the va-

XX nVTRODVCTION.

rious textures of the body. That besides certain characteristic physical properties, it disphiys others that neither chemical nor mechanical laws can adequately account for, and which it is conceived must depend upon its vitality. We shall then advert to the function of Ah~ sorption^ and endeavour to point out the means whereby not only fresh materials are introduced, but also how the various worn-out and decayed parts are taken up from the different parts of the system.

Here we shall have to examine a subordinate set of vessels that arise from every organ, and every tissue of the body, of a peculiar structure, exceedingly numerous, freely communicating with each other, and ultimately terminating in the red veins, before these reach the heart. By the action of these vessels, the AbsorhenUy and by other means, the superfluous and decayed parts are carried off, subsequently either to be renovated, or to be altogether rejected and cast out of the body.

The last of the conservative series of functions is Secre-- turn. Under this head we shall direct our attention to the various fluids elaborated from the blood, and the character and mode of action of the instruments by which they are furnished, as well as the purposes they serve, either in freeing the system from superfluous or noxious matters, or as they contribute to other useful ends. Some of these fluids are to be considered chiefly, if not entirely, as excrementitious, their evacuation being subservient to the purification of the body by the removal of the decayed and redundant parts. Of this kind are the vapours extricated from the breath, the matter of perspiration from the external surface, several of the secretions poured into the intestinal canal, and the urine derived from the action of the kidneys. Others, again, are furnished for particular purposes, — as the tears to moisten the eyes ; the saliva to mix with the food ; the gastric juice, an important agent in digestion ; the bile, to excite the intestines, and to aid in the elaboration of the chyle ; and several others, regarding which it is necessary not only to consider

INTRODUCTION. XXI

how the secretion is famished, and the nature of its constitution, but likewise its appUcation to other operations.

Lastly, since from the commencement of life to its termination, the component parts of the body are neyer the same, but constantly receiving fresh accessions of matter, and rejecting the old and decayed particles, numerous vessels are incessantly engaged in the secretion of the various textures composing thedi£Eerent organs of the body. Thus, in bone the osseous tissue is secreted; in muscle the muscular fibre; in glands their peculiar tissues, and so forth. In every individual part the vessels furnish the characteristic matter required in due quantity, and with the necessary quickness of renewal. After examining the various conservative organs and functions, we shall next turn our attention to ^ose of relation.