Mind Amongst the Spindles — A Conversation on Physiology
H.
F.
A CONVERSATION ON PHYSIOLOGY.
INTRODUCTION.
Physiology, Astronomy, Geology, Botany, and kindred sciences, are not now, as formerly, confined to our higher seminaries of learning.
They are being introduced into the common schools, not only of our large towns and cities, but of our little villages throughout New-England.
Hence a knowledge of these sciences is becoming general.
It needs not Sibylline wisdom to predict that the time is not far distant when it will be more disadvantageous and more humiliating to be ignorant of their principles and technicalities, than to be unable to tell the length and breadth of Sahara, the rise, course and fall of little rivers in other countries, which we shall never see, never hear mentioned--and the latitude and longitude of remote or obscure cities and towns.
If a friend would describe a flower, she would not tell us that it has so many flower-leaves, so many of those shortest things that rise from the centre of the flower, and so many of the longest ones; but she will express herself with more elegance and rapidity by using the technical names of these parts--petals, stamens, and pistils.
She will not tell us that the green leaves are formed some like a rose-leaf, only that they are rounder, or more pointed, as the case may be; or if she can find no similitudes, she will not use fifty words in conveying an idea that might be given in one little word.
We would be able to understand her philosophical description.
And scientific lectures, the sermons of our best preachers, and the conversation of the intelligent, presuppose some degree of knowledge of the most important sciences; and to those who have not this knowledge, half their zest is lost.
If we are so situated that we cannot attend school, we have, by far the greater part of us, hours for reading, and means to purchase books.
We should be systematic in our expenditures.
They should be regulated by the nature of the circumstances in which we find ourselves placed,--by our wages, state of health, and the situation of our families.
After a careful consideration of these, and other incidentals that may be, we can make a periodical appropriation of any sum we please, for the purchase of books.
Our readings, likewise, should be systematic.
If we take physiology, physiology should be read exclusively of all others, except our Bibles and a few well-chosen periodicals, until we acquire a knowledge of its most essential parts.
Then let this be superseded by others, interrupted in their course only by occasional reviews of those already studied.
But there are those whose every farthing is needed to supply themselves with necessary clothing, their unfortunate parents, or orphan brothers and sisters with a subsistence.
And forever sacred be these duties.
Blessings be on the head of those who faithfully discharge them, by a cheerful sacrifice of selfish gratification.
Cheerful, did I say?
Ah!
many will bear witness to the pangs which such a sacrifice costs them.
It is a hard lot to be doomed to live on in ignorance, when one longs for knowledge, "as the hart panteth after the water brook."
My poor friend L.' s complaint will meet an answering thrill of sympathy in many a heart.
"Oh, why is it so?"
said she, while tears ran down her cheeks.
"Why have I such a thirst for knowledge, and not one source of gratification?"
We may not know _why_, my sister, but faith bids us trust in God, and "rest in his decree,"--to be content "when he refuses more."
Yet a spirit of _true_ contentment induces no indolent yieldings to adverse circumstances; no slumbering and folding the hands in sleep, when there is so much within the reach of every one, worthy of our strongest and most persevering efforts.
Mrs. Hale says,-- "There is a charm in knowledge, _best_ when bought _By vigorous toil of frame and earnest search of thought_."
And we will toil.
Morning, noon, and evening shall witness our exertions to prepare for happiness and usefulness here, and for the exalted destiny that awaits us hereafter.
But proper attention should be paid to physical comfort as well as to mental improvement.
It is only by retaining the former that we can command the latter.
The mind cannot be vigorous while the body is weak.
Hence we should not allow our toils to enter upon those hours which belong to repose.
We should not allow ourselves, however strong the temptation, to visit the lecture-room, &c. , if the state of the weather, or of our health, renders the experiment hazardous.
Above all, we should not forget our dependence on a higher Power.
"Paul may plant, and Apollos water, but God alone giveth the increase."
* * * * * _Ann.
_ Isabel, before we commence our "big talk," let me ask you to proceed upon the inference that we are totally ignorant of the subject under discussion.
_Ellinora.
_ Yes, Isabel, proceed upon the _fact_ that I am ignorant even of the meaning of the term _physiology_.
_Isabel.
_ It comes from the Greek words _phusis_, nature, and _logia_, a collection, or _logos_, discourse; and means a collection of facts or discourse relating to nature.
Physiology is divided, first, into Vegetable and Animal; and the latter is subdivided into Comparative and Human.
We shall confine our attention to Human Physiology, which treats of the organs of the human body, their mutual dependence and relation, their functions, and the laws by which our physical constitution is governed.
_A.
_ And are you so heretical, dear Isabel, as to class this science, on the score of utility, with Arithmetic and Geography--the alpha and omega of common school education?
_I.
_ Yes.
It is important, inasmuch as it is necessary that we know how to preserve the fearfully delicate fabric which our Creator has entrusted to our keeping.
We gather many wholesome rules and cautions from maternal lips; we learn many more from experiencing the painful results that follow their violation.
But this kind of knowledge comes tardily; it may be when an infringement of some organic law, of which we were left in ignorance, has fastened upon us painful, perhaps fatal, disease.
_A.
_ We may not always avoid sickness and premature death by a knowledge and observance of these laws; for there are hereditary diseases, in whose origin we are not implicated, and whose effects we cannot eradicate from our system by "all knowledge, all device."
_I.
_ But a knowledge of Physiology is none the less important in this case.
If the chords of our existence are shattered, they must be touched only by the skilful hand, or they break.
_E.
_ Were it not for this, were there no considerations of utility in the plea, there are others sufficiently important to become impulsive.
It would be pleasant to be able to trace the phenomena which we are constantly observing within ourselves to their right causes.
_I.
_ Yes; we love to understand the springs of disease, even though "a discovery of the cause" neither "suspends the effect, nor heals it."
We rejoice in health, and we love to know why it sits so strongly within us.
The warm blood courses its way through our veins; the breath comes and goes freely in and out; the nerves, those subtle organs, perform their important offices; the hand, foot, brain--nay, the whole body moves as we will: we taste, see, hear, smell, feel; and the inquiring mind delights in knowing by what means these wonderful processes are carried on,--how far they are mechanical, how far chemical, and how far resolvable into the laws of vitality.
This we may learn by a study of Physiology, at least as far as is known.
We may not satisfy ourselves upon all points.
There may be, when we have finished our investigations, a longing for a more perfect knowledge of ourselves; for "some points must be greatly dark," so long as mind is fettered in its rangings, and retarded in its investigations by its connection with the body.
And this is well.
We love to think of the immortal state as one in which longings for moral and intellectual improvement will _all_ be satisfied.
_A.
_ Yes; it would lose half its attractions if we might attain perfection here.
_E.
_ And now permit me to bring you at once to our subject.
What is this life that I feel within me?
Does Physiology tell us?
It ought.
_I.
_ It does not, however; indeed, it cannot.
It merely develops its principles.
_E.
_ The principles of life--what are they?
_I.
_ The most important are _contractibility_ and _sensibility_.
_E.
_ Let me advertise you that I am particularly hostile to technical words--all because I do not understand them, I allow, but please humor this ignorance by avoiding them.
_I.
_ And thus perpetuate your ignorance, my dear Ellinora?
No; this will not do; for my chief object in these conversations is that you may be prepared to profit by lectures, essays and conversation hereafter.
You will often be thrown into the company of those who express themselves in the easiest and most proper manner, that is, by the use of technical words and phrases.
These will embarrass you, and prevent that improvement which would be derived, if these terms were understood.
Interrupt me as often as you please with questions; and if we spend the remainder of the evening in compiling a physiological glossary, we may all reap advantage from the exercise.
To return to the vital principles--vital is from _vita_, life--_contractibility_ and _sensibility_.
The former is the property of the muscles.
The muscles, you know, are what we call flesh.
They are composed of fibres, which terminate in tendons.
_Alice.
_ Please give form to my ideas of the tendons.
_I.
_ With the muscles, they constitute the agents of all motion in us.
Place your hand on the inside of your arm, and then bend your elbow.
You perceive that cord, do you not?
That is a tendon.
You have observed them in animals, doubtless.
_Ann.
_ I have.
They are round, white, and lustrous; and these are the muscular terminations.
_I.
_ Yes; this tendon which you perceive, is the termination of the muscles of the fore-arm, and it is inserted into the lower arm to assist in its elevation.
_E.
_ Now we are coming to it.
Please tell me how I move a finger--how I raise my hand in this manner.
_I.
_ It is to the contractile power of the muscles that you are indebted for this power.
I will read what Dr. Paley says of muscular contraction;
it will make it clearer than any explanation of mine.
He says, "A muscle acts only by contraction.
Its force is exerted in no other way.
When the exertion ceases, it relaxes itself, that is, it returns by relaxation to its former state, but without energy."
_E.
_ Just as this India-rubber springs back after extension, for illustration.
_I.
_ Very well, Ellinora.
He adds, "This is the nature of the muscular fibre; and being so, it is evident that the reciprocal _energetic_ motion of the limbs, by which we mean _with force_ in opposite directions, can only be produced by the instrumentality of opposite or antagonist muscles--of flexors and extensors answering to each other.
For instance, the biceps and brachiæus _internus_ muscles, placed in the front part of the upper arm, by their contraction, bend the elbow, and with such a degree of force as the case requires, or the strength admits.
The relaxation of these muscles, after the effort, would merely let the fore-arm drop down.
For the _back stroke_ therefore, and that the arm may not only bend at the elbow, but also extend and straighten itself with force, other muscles, the longus, and brevis brachiæus _externus_, and the aconæus, placed on the hinder part of the arms, by their contractile twitch, fetch back the fore-arm into a straight line with the cubit, with no less force than that with which it was bent out.
The same thing obtains in all the limbs, and in every moveable part of the body.
A finger is not bent and straightened without the _contraction_ of two muscles taking place.
It is evident, therefore, that the animal functions require that particular disposition of the muscles which we describe by the name of antagonist muscles."
_A.
_ Thank you, Isabel.
This does indeed make the subject very plain.
These muscles contract at will.
_E.
_ But how can the will operate in this manner?
I have always wished to understand.
_I.
_ And I regret that I cannot satisfy you on this point.
If we trace the cause of muscular action by the nerves to the brain, we are no nearer a solution of the mystery; for we cannot know what power sets the organs of the brain at work--whether it be foreign to or of itself.
We will come now, if you please to _sensibility_, which belongs to the nerves.
_A.
_ I have a very indefinite idea of the nerves.
_E.
_ My _ideal_ is sufficiently definite in its shape, but so droll!
I
do not think of them as "being flesh of my flesh," but as a _species_ of the _genus_ fairy.
They are to us, what the Nereides are to the green wave, the Dryades to the oak, and the Hamadryades to the little flower.
They are quite omnipotent in their operations.
They make us cry or they make us laugh; thrill us with rapture or woe as they please.
And, my dear Isabel, I shall not allow you to cheat me out of this pleasing fancy.
You may tell us just what they are, but I shall be as incredulous as possible.
_I.
_ They are very slender white cords, extending from the brain and spinal marrow--twelve pairs from the former, and thirty from the latter.
These send out branches so numerous that we cannot touch the point of a pin to a spot that has not its nerve.
The mucous membrane is-- _F.
_ Oh, these technicals!
What is the mucous membrane?
_I.
_ It is a texture, or web of fibres, which lines all cavities exposed to the atmosphere--for instance, the mouth, windpipe and stomach.
It is the seat of the senses of taste and smell.
_E.
_ And the nerves are the little witches that inform the brain how one thing is sweet, another bitter; one fragrant, another nauseous.
Alimentiveness ever after frowns or smiles accordingly.
So it seems that the actions of the brain, and of the external senses, are reciprocated by the nerves, or something of this sort.
How is it, Isabel?
Oh, I see!
You say sensibility belongs to the nerves.
So sights by means of--of what?
_I.
_ Of the optical nerves.
_E.
_ Yes; and sounds by means of the-- _I.
_ Auditory nerves.
_E.
_ Yes; convey impressions of externals to the brain.
And "Upon this hint" the brain acts in its consequent reflections, and in the nervous impulses which induce muscular contractibility.
And this muscular contractibility is a contraction of the fibres of the muscles.
This contraction, of course, shortens them, and this latter _must_ result in the bending of the arm.
I think I understand it.
What are the brain and spine, Isabel?
How are they connected?
_I.
_ You will get correct ideas of the texture of the brain by observing that of animals.
It occupies the whole cavity of the skull, is rounded and irregular in its form, full of prominences, _alias_ bumps.
These appear to fit themselves to the skull; but doubtless the bone is moulded by the brain.
The brain is divided into two parts; the upper and frontal part is called the _cerebrum_, the other the _cerebellum_.
The former is the larger division, and is the seat of the moral sentiments and intellectual faculties.
The latter is the seat of the propensities, domestic and selfish.
_A.
_ I thank you, Isabel.
Now, what is this spine, of which there is so much "complaint" now-a-days?
_I.
_ I will answer you from Paley: "The spine, or backbone, is a chain of joints of very wonderful construction.
It was to be firm, yet flexible; _firm_, to support the erect position of the body; _flexible_, to allow of the bending of the the trunk in all degrees of curvature.
It was further, also, to become a pipe or conduit for the safe conveyance from the brain of the most important fluid of the animal frame, that, namely, upon which _all voluntary motion depends, the spinal marrow_; a substance not only of the first necessity to action, if not to life, but of a nature so delicate and tender, so susceptible and impatient of injury, that any unusual pressure upon it, or any considerable obstruction of its course, is followed by paralysis or death.
Now, the spine was not only to furnish the main trunk for the passage of the medullary substance from the brain, but to give out, in the course of its progress, small pipes therefrom, which, being afterwards indefinitely subdivided, might, under the name of nerves, distribute this exquisite supply to every part of the body."
_Alice.
_ I understand now why disease of the spine causes such involuntary contortions and gestures, in some instances.
Its connection with the brain and nerves is so immediate, that it cannot suffer disease without affecting the whole nervous system.
_I.
_ It cannot.
The spinal cord or marrow is a continuation of the brain.
But we must not devote any more time to this subject.
_Bertha.
_ I want to ask you something about the different parts of the eye, Isabel.
When ---- ---- lectured on optics, I lost nearly all the benefit of his lecture, except a newly awakened desire for knowledge on this subject.
He talked of the retina, cornea, iris, &c. ; please tell me precisely what they are.
_I.
_ The retina is a nervous membrane; in other words a thin net-work, formed of very minute sensitive filaments.
It is supposed by some to be an expansion of the optic nerve; and on this the images of objects we see are formed.
It is situated at the back part of the eye.
Rays pass through the round opening in the iris, which we call the pupil.
_B.
_ What did the lecturer say is the cause of the color of the pupil?
_I.
_ He said that its _want of color_ is to be imputed to the fact that rays of light which enter there are not returned; they fall on the retina, forming there images of objects.
And you recollect he said that "absence of rays is blackness."
The iris is a kind of curtain, covering the aqueous humor--aqueous is from the Latin _aqua_, water.
It is confined only at its outer edge, or circumference; and is supplied with muscular fibres which confer the power of adjustment to every degree of light.
It contracts or dilates involuntarily, as the light is more or less intense, as you must have observed.
The rays of light falling on that part of the iris which immediately surrounds the pupil, cause it to be either black, blue, or hazel.
We will not linger on this ground, for it belongs more properly to Natural Philosophy.
We will discuss the other four senses as briefly as possible.
"The sense of taste," says Hayward, "resides in the mucus membrane of the tongue, the lips, the cheeks, and the fauces."
Branches of nerves extend to every part of the mouth where the sense of taste resides.
The fluid with which the mouth is constantly moistened is called mucus, and chiefly subserves to the sense of taste.
_Ann.
_ I have observed that when the mucus is dried by fever, food is nearly tasteless.
I now understand the reason.
_E.
_ _Apropos_ to the senses, let me ask if feeling and touch are the same.
Alfred says they are; I contend they are not, precisely.
_I.
_ Hayward thinks a distinction between them unnecessary.
He says they are both seated in the same organs, and have the same nerves.
But the sense of feeling is more general, extending over the whole surface of the skin and mucus membrane, while that of touch is limited to particular parts, being in man most perfect in the hand; and the sense of feeling is passive, while that of touch is active.
This sense is in the skin, and is most perfect where the epidermis, or external coat, is the thinnest.
We will look through this little magnifying glass at the skin on my hand.
You will see very minute prominences all over the surface.
These points are called papillæ.
They are supposed to be the termination of the nerves, and the _locale_ of sensation.
_E.
_ Will you _shape_ my ideas of sensation?
_I.
_ According to Lord Brougham, one of the English editors of this edition of Paley, it is "the effect produced upon the mind by the operation of the senses; and involves nothing like an exertion of the mind itself."
Of the sense of hearing, I can tell you but little.
Physiologists have doubts relative to many parts of the ear; and I do not understand the subject well enough to give you much information.
I will merely name some of the parts and their relative situations.
We have first the external ear, which projecting as it does from the head, is perfectly adapted to the office of gathering sounds, and transmitting them to the membrane of the tympanum, commonly called the drum of the ear, from its resembling somewhat, in its use and structure, the head of a drum.
The tympanum is a cavity, of a cylindrical or tunnel form, and its office is supposed to be the transmission to the internal ear of the vibrations made upon the membrane.
These vibrations are first communicated to the malleus or hammer.
This is the first of four bones, united in a kind of chain, extending and conveying vibrations from the tympanum to the labyrinth of the ear beyond.
The other bones are the incus, or anvil, the round bone, and the stapes, or stirrup--the latter so called from its resemblance to a stirrup-iron.
It is placed over an oval aperture, which leads to the labyrinth, and which is closed by means of a membranous curtain.
These bones are provided with very small muscles, and move with the vibrations of the tympanum.
The equilibrium of the air in the tympanum and atmosphere is maintained by the means of the Eustachian tube, which extends from the back part of the fauces, or throat, to the cavity of the tympanum.
The parts last mentioned constitute the middle ear.
Of the internal ear little is known.
It has its semicircular canals, vestibules, and cochlea; but their agencies are not ascertained.
The organ of smell is more simple.
This sense lies, or is supposed to lie, in the mucous membrane which lines the nostrils and the openings in connection.
Particles are constantly escaping from odorous bodies; and, by being inhaled in respiration, they are thrown in contact with the mucous membrane.
_A.
_ Before leaving the head, will you tell us something of the organs of voice?
_I.
_ By placing your finger on the top of your windpipe, you will perceive a slight prominence.
In males this is very large.
This is the thorax.
It is formed of four cartilages, two of which are connected with a third, by means of four chords, called vocal chords, from their performing an important part in producing the voice.
Experiments have been made, which prove that a greater part of the larynx, except these chords, may be removed without destroying the voice.
Magendie thus accounts for the production of the voice.
He says, "The air, in passing from the lungs in expiration, is forced out of small cavities, as the air-cells and the minute branches of the windpipe, into a large canal;
it is thence sent through a narrow passage, on each side of which is a vibratory chord, and it is by the action of the air on these chords, that the sonorous undulations are produced which are called voice."
_E.
_ Do not the lips and tongue contribute essentially to speech?
_I.
_ They do not.
Hayward says he can bear witness to the fact that the articulation remains unimpaired after the tongue has been removed.
The labials, _f_ and _v_, cannot be perfectly articulated without the action of the lips.
--What subject shall we take next?
_A.
_ A natural transition would be from the head to the heart, and, in connection, the circulation of the blood.
_I.
_ Yes.
I will give you an abstract of the ideas I gained in the study of Hayward's Physiology, and the reading of Dr. Paley's Theology.
The heart, arteries, and veins are the agents of circulation.
The heart is irregular and conical in its shape; and it is hollow and double.
_A.
_ There is no channel of communication between these parts, is there?
_I.
_ None; but each side has its separate office to perform.
By the right, circulation is carried on in the lungs; and by the left through the rest of the body.
I will mark a few passages in Paley, for you to read to us, Ann.
They will do better than any descriptions of mine.
_A.
