Chapter 2

The more violently the exciting powers have acted, the sooner is sleep brought on; because the excitability is sooner exhausted, and therefore, sooner requires the means of renewing it; and on the contrary, the more weakly the exciting powers have acted, the less is a person inclined to sleep. Instances of the first are, excess of exercise, strong liquors, or study, and of the latter, an under proportion of these.

A person who has been daily accustomed to much exercise, whether mental or corporeal, if he omit it, will find little or no inclination to sleep; he may however be made to sleep by taking a little diffusible stimulus; for instance, a little warm punch, or opium: these act entirely by exhausting the excitability to that degree which is compatible with sleep; and when their stimulant effect is over, the person soon falls into that state.

But though the excitability may have been sufficiently exhausted, and the action of the external powers considerably moderated, yet there are some things within ourselves, which stimulate violently, and prevent sleep; such as pain, thirst, and strong passions and emotions of the mind. These all tend to drive away sleep, but it may be induced, by withdrawing the mind from these impressions; particularly from uneasy emotions, and employing it on something which makes a less impression; sleep, in such cases, is frequently brought on by listening to the humming of bees, [1] or the murmuring of a rivulet; by employing the mind on subjects which do not require much exertion, nor produce too much commotion; such as counting to a thousand, or counting drops of water which fall slowly.

It sometimes happens, as has been well observed by Dr. Franklin, that an uneasy heat of the skin, from a want of perspiration, occasioned by the heat of the bed-cloaths, will prevent sleep; in this case, he recommends a method, which I believe will often succeed--namely, to get up and walk about the room till you are considerably cooled; when you get into bed again, the heat of the skin will be diminished, and perspiration become more free, and you will probably sleep in a very few minutes. [2]

By induction we have discovered two of the principal laws by which living bodies are governed; the first is, that when the ordinary powers which support life have been suspended, or their action lessened for a time, the excitability, or vital principle accumulates, or becomes more fit to receive their actions; and secondly, when these powers have been acted upon violently, or for a considerable time, the excitability is exhausted, or becomes less fit to receive their actions. There are therefore three states in which living bodies exist.--

First, a state of accumulated excitability.

Second, a state of exhausted excitability.

Third, when it is in such a state as to produce the strongest and most healthy actions, when acted upon by the external powers.

From what I have said, it must appear, that life is a forced state, depending on the action of external powers upon the excitability; and that, by their continued action, if they are properly regulated, the excitability will be gradually and insensibly exhausted; and life will be resigned into the hands of him who gave it, without a struggle, and without a groan.

We see then, that nature operates in supporting the living part of the creation, by laws as simple and beautiful as those by which the inanimate world is governed. In the latter we see the order and harmony which is observed by the planets, and their satellites, in their revolution round the great source of heat and light.

'-----All combin'd 'and ruled unerring, by that single power 'which draws the stone projected, to the ground.'

In the animated part of the creation, we observe those beautiful phenomena which are exhibited by an almost infinite variety of individuals, all depending upon one simple law, the action of the exciting powers on the excitability.

I cannot express my admiration of the wisdom of the creator better than in the words of Thomson.

'O unprofuse magnificence divine! 'O wisdom truly perfect! thus to call 'from a few causes, such a scheme of things; 'effects so various, beautiful, and great.'

Life then, or those functions which we call living, are the effects of certain exciting powers, acting on the excitability, or property distinguishing living from dead matter. When those effects, namely, the functions, flow easily, pleasantly, and completely, from the action of the exciting powers, they indicate that state which we call Health.

I have detained you a long time on this subject, but it is of importance to make you acquainted with these laws; for it is from a knowledge of them, that the rules for preserving health must be deduced; and having rendered them, as I hope, intelligible to you, I shall proceed to point out such necessary cautions for your conduct, as are easily deduced from them; and which experience confirms; and I shall follow an arrangement in the consideration of the subject, which naturally presents itself to us. The chief exciting powers which act upon us are, air and food; these I shall respectively consider, and afterwards make a few remarks on exercise.

The air is the main-spring in the animal machine; the source of heat and activity, without which our blood would soon become a black and stagnant mass, and life would soon stop.

It is now known, that only a part of atmospheric air, is necessary for respiration: the atmosphere near the surface of the earth, consists of two kinds of air; one, which is highly proper for respiration, and combustion, and in which, an animal immersed, will live much longer than in the same quantity of common air; and one, which is perfectly improper for supporting respiration, or combustion, for an instant.

The first of these airs, has been called vital air, from its property of supporting life, and constitutes about one fourth of the atmosphere. [3] The other, from its property of destroying life, is called azote, and forms of course the remaining three fourths of the atmosphere.

These two airs may be separated from each other by various methods. If a candle be inclosed in a given quantity of atmospheric air, it will burn only for a certain time, and then be extinguished; and from the rising of the water in the vessel in which it is inclosed, it is evident that a quantity of air has been absorbed. What has been absorbed is the vital air, and what remains, the azote, which is incapable of supporting flame. If an animal be immersed in a given quantity of common air, it will live only a certain time; at the end of this time, the air will be found diminished, about one fourth being extracted from it, and the remainder will neither support flame nor animal life; this experiment might easily be made, but it seems a piece of unnecessary cruelty.

By similar experiments to those I have mentioned, we get the azote pure; here is some, in which a candle has burnt out, and in which nothing but azote, or the impure part of the atmosphere is left. [4] I shall plunge a lighted match into it, and you see it is instantly extinguished.

Some metals, and particularly manganese, when exposed to the atmosphere, attract the vital air from it, without touching the azote; and it may be procured from these metals by the application of heat, in very great purity. Here is a bottle of that kind of air, which I have expelled by heat from manganese; I shall plunge a taper into it, and you will perceive that it burns with great brilliancy. An animal shut up in it, would live about four times as long as if shut up in an equal quantity of atmospheric air.

If I take three parts of azote, and one of vital air, I shall form a compound which is similar to the atmosphere, and which is the mixture best suited to support the health of the body; for if there were a much greater proportion of vital air, it would act too powerfully upon the system, and bring on inflammatory diseases; it would likewise by its stimulus exhaust the excitability, and bring us sooner to death; and in the same manner that a candle burns brighter in vital air, and would therefore be sooner exhausted, so would the flame of life be sooner burnt out.

On the contrary, if the atmosphere contained a much less proportion of vital air, it would not stimulate the body sufficiently; the excitability would morbidly accumulate, and diseases of debility would occur.

Combustion, putrefaction, and the breathing of animals, are processes which are continually diminishing the quantity of vital air contained in the atmosphere; and if the all-wise author of nature had not provided for its continual re-production, the atmosphere would in all probability have long since become too impure to support life; but this is guarded against in a most beautiful manner.

Water is not a simple element, as has been supposed, but is composed of vital air, and a particular kind of air which is called _inflammable_; the same that is used to fill balloons. It has been found by experiment, that one hundred pounds of water, are composed of eighty-five pounds of vital air, and fifteen of inflammable air. [5]

Water may be decompounded by a variety of means, and its component parts separated from each other.

Vegetables effect this decomposition; they absorb water, and decompose it in their glands; and taking the inflammable air for their nourishment, breathe out the vital air in a state of very great purity; this may be ascertained by a very easy experiment.

This vital air is received by animals into their lungs, gives them their heat, and communicates a red colour to their blood; when animals die for want of vital air, their blood is always found black.

From what I have said, it is evident, that in large and populous towns, where combustion and respiration are continually performed on a large scale, the air must be much less pure than in the country, where there are few of these causes to contaminate the atmosphere, and where vegetables are continually tending to render it more pure; and if it was not for the winds which agitate this element, and constantly occasion its change of place, the air of large towns would probably soon become unfit for respiration. Winds bring us the pure air of the country, and take away that from which the vital air has been in a great measure extracted; but still, from the immense quantity of fuel which is daily burnt, and the number of people breathing in large towns, the air very soon becomes impure.

From the greater purity of the air in the country, proceeds the rosy bloom found in the rural cottage, which we in vain look for in the stately palace, or the splendid drawing room. Here then are reasons for preferring the country, which no one will dispute, and whenever it can be done, such a situation ought always to be chosen in preference to a large town: this cannot be better enforced than in the words of Dr. Armstrong.--

'Ye, who amid the feverish world would wear 'a body free of pain, of cares a mind; 'fly the rank city, shun its turbid air; 'breathe not the chaos of eternal smoke, 'and volatile corruption, from the dead, 'the dying, sick'ning, and the living world 'exhaled, to sully heaven's transparent dome 'with dim mortality.

'While yet you breathe, away; the rural wilds 'invite; the mountains call you, and the vales; 'the woods, the streams, and each ambrosial breeze 'that fans the ever undulating sky.'

But there are many whose occupations oblige them to reside in large towns; they, therefore, should make frequent excursions into the country, or to such situations as will enable them to enjoy, and to breathe air of a little more purity. I say _enjoy_, for who that has been for some time shut up in the town, without breathing the pure air of the country, does not feel his spirits revived the moment he emerges from the azote of the town. Let not therefore, if possible, a single day pass, without enjoying, if but for an hour, the pure air of the country. Doing this, only for a short time _every_ day, would be much more effectual than spending whole days, or even weeks in the country, and then returning into the corrupt atmosphere of the town; for when you have for a long time breathed an impure air, the excitability becomes so morbidly accumulated, from the want of the stimulus of pure air, that the air of the country will have too great an effect upon you; it will frequently, in the course of a day or two, bring on an inflammatory fever, attended with stuffing of the nose, hoarseness, a great degree of heat, and dryness of the skin, with other symptoms of a violent cold.

Large towns are the graves of the human species; they would perish in a few generations, if not constantly recruited from the country. The confined, putrid air, which most of their inhabitants breathe, their want of natural exercise, but above all their dissipation, shorten their lives, and ruin their constitutions.

Children particularly, require a pure air; every circumstance points out the country as the proper place for their education; the purity of the air, the variety of rustic sports, the plainness of diet, the simplicity and innocence of manners, all concur to recommend it. It is a melancholy fact, that above half the children born in London, die before they are two years old.

To shew how indispensable fresh air is to children, I shall mention one example which sets the fact in the clearest light. In the lying-in hospital at Dublin, 2944 infants, out of 7650, died in the year 1782, within the first fortnight after their birth, which is nearly every third child; they almost all died in convulsions; many of them foamed at the mouth, their thumbs were drawn into the palms of their hands, their jaws were locked, the face was swelled and looked blue, as though they were choaked. This last circumstance led the physicians to conclude that the rooms in the hospital were too close, and hence, that the infants had not a sufficient quantity of good air to breathe; they therefore set about ventilating them better, which was done very completely. The consequence has been, that not one child dies now where three used to die.

Fewer children indeed die convulsed now, than formerly; this is because the rich learn, either from books, or conversation with physicians, how necessary fresh air is to life and health; hence they keep their houses well aired; but the poor, and servants, are not made to comprehend this matter properly; and therefore from neglecting to open their windows, and breathing a foul, tainted air, the greatest part of their time, many disorders are brought on, and others rendered worse than they naturally would be. [6]

Having considered the purity of the air, let us next take a view of the changes in temperature which it undergoes, and the effects which these have upon the constitution.

We find the air sometimes considerably below the freezing point; nay, even so much as 20 or 30 degrees; it is then intensely cold; and on the other hand, the thermometer sometimes indicates a great degree of heat. We then find ourselves much relaxed, and our constitutions exhausted.

To understand how this happens, let us consider for a moment the nature of heat, and cold.--Heat is one of those stimuli which act upon the excitability, and support life: for if it was totally withdrawn, we should not be able to exist even a few minutes; and cold is only a diminution of heat. When heat is present, in a proper degree, or the atmosphere is about that degree of heat which we call temperate, it just gives such a stimulus, and keeps the excitability exhausted to such a degree, as to preserve the body in health; but if it continue for a considerable time to be much warmer than this temperature, the consequence must be, from the laws already laid down, an exhaustion of the excitability, and a consequent relaxation and debility; for, when the excitability has been exhausted by the violent application of heat, long continued, the common stimulant powers which support life, cannot produce a sufficient effect upon it, to give to the body that tone which is compatible with health. On the contrary, when the heat of the air falls below what we call temperate, or when cold is applied to the body, from the accustomed stimulus of heat being diminished, the excitability must accumulate, or become more liable to be affected by the action of the external powers.

This, however, very seldom produces bad effects, unless the exciting powers be improperly or quickly applied; for we can bear a considerable diminution of heat without any bad consequences; and in all cases I hope I shall be able to make it appear, that much more mischief arises from the too great action of heat, than from the diminution of it. Nature never made any country too cold for its inhabitants. In cold climates, she has made exercise, and even fatigue habitual to them, not only from the necessity of their situation, but from choice; their natural diversions being all of the athletic or violent kind. But the softness and effeminacy of modern manners, has both deprived us of our natural defence against the diseases most incident to our climate, and subjected us to all the inconveniencies of a warm one.

People are afraid of going out into the cold air; but if they conduct themselves properly afterwards, they will never be in the least danger from it. Indeed the action of cold, unless it be excessive, never produces any bad effects.

Many of you will, no doubt, think me here in an error; but I hope you will not long entertain that opinion. You will say that you have had frequent experience to the contrary; that you have often gone out into the cold air, and have caught dreadful colds. That this is owing to the action of cold, I will deny; nay, I will assert, that if a person go out into air which is very cold, _and remain in it_ for a very long time, he will never perceive any symptoms of what is called a cold so long as he remains there.

A common cold is attended with a running of the nose, hoarseness, and cough, with a considerable degree of feverish heat, an dryness of the skin.--Now it is universally agreed, that this disorder is an inflammation, or is of an inflammatory nature; it is an inflammation of the smooth, moist skin which lines the nostrils, and goes down the wind-pipe into the lungs; but as cold is only a diminution of heat, or a diminution of a stimulus acting upon the body, it is impossible that such a diminution can cause a greater action or excitement; we might as well expect to fill a vessel by taking water out of it. But let us see how a cold, as it is commonly called, is usually produced. When a person in cold weather goes out into the air, every time he draws in his breath, the cold air passes through his nostrils and windpipe into the lungs, and in thus diminishing the heat of the parts, allows their excitability to accumulate, and renders them more liable to be affected by the succeeding heat. So long as that person continues in the cold air, he feels no bad effects; but if he come into a warm room, he first perceives a glow within his nostrils and breast, as well as all over the surface of the body. Soon afterwards, a disagreeable dryness and huskiness will be felt in the nostrils and breast. By and by a short, dry, tickling cough comes on. He feels a shivering, which makes him draw nearer to the fire, but all to no purpose; the more he tries to heat himself, the more chill he becomes. All the mischief is here caused by the violent action of the heat on the accumulated excitability. For want of a knowledge of this law, these disagreeable, and often dangerous complaints are brought on; when they might be avoided with the greatest ease.

When you take a ride into the country on a cold day, you find yourselves very cold; as soon as you go into a house, you are invited to come to the fire, and warm yourselves; and what is still worse, to drink something warm and comfortable, to keep out the cold, as the saying is. The inevitable consequence of this, is, to bring on the complaints which I have just described, which might with more propriety be called, heats than colds. But how easily might these complaints have been avoided! When you come out of a very cold atmosphere, you should not at first go into a room that has a fire in it, or if you cannot avoid that, you should keep for a considerable time at as great a distance from the fire as possible, that the accumulated excitability may be gradually exhausted, by the moderate and gentle action of heat; and then you may bear the heat of the fire without any danger: but, above all, refrain from taking warm or strong liquors while you are cold. If a person have his hands or feet exposed to a very severe cold, the excitability of those parts will be so much accumulated, that if they should be brought suddenly near the fire, a violent inflammation, and even a mortification will take place, which has often happened; or, at any rate, that inflammation called Chilblains will be produced, from the violent action of the heat upon the accumulated excitability of those parts; but, if a person so circumstanced, was to put his hands or feet into cold water, very little warmer than the atmosphere to which he had been exposed, or rub them with snow, which is not often colder than 32 or 30 degrees, the morbid excitability will be gradually exhausted, and no bad consequences will ensue.

When a part of the body only has been exposed to the action of cold, and the rest kept heated; if, for instance, a person in a warm room sits so that a current of air coming through a broken pane, should fall upon any part of the body, that part will be soon affected with an inflammation, which is usually called a rheumatic inflammation. From what has been said, it will be easy to account for this circumstance. The excitability of the part is accumulated by the diminution of its heat; but at the same time, the rest of the body and blood is warm; and this warm blood acting upon a part where the excitability is accumulated, will cause an inflammation; to which, the more you apply heat, the worse you make it.--From these considerations, we may lay it down as a fact, and experience supports us in so doing, that you may in general go out of warm into cold air without much danger; but, that you can never return suddenly from the cold into the warm air with perfect impunity.

Hence, we may lay down the following rule, which, if strictly observed, would prevent the frequent colds we meet with in winter. _When the whole body, or any part of it, is chilled, bring it to its natural feeling and warmth by degrees._

But if, for want of observing this necessary caution, a cold, as it is called, should have seized a person, let us consider what is proper to be done.

It will, from the preceding reasoning, appear very improper to make the room where you sit warmer than usual, to increase the quantity of bed-clothes, to wrap yourself up in flannel, or particularly to drink a large quantity of barley-water, gruel, or tea, almost boiling hot, by way of diluting, as it is called, and forcing a perspiration; this will infallibly make the disorder worse, in the same manner as confining inoculated persons in warm rooms would make their small-pox more violent.

Perhaps there would be scarcely such a thing as a bad cold, if people, when they found it coming on, were to keep cool, and avoid wine and strong liquors, and confine themselves for a short time to a simple diet of vegetable food, drinking only toast and water. Instances are by no means uncommon, where a heat of the nostrils, difficulty of breathing, a short, tickling cough, and other symptoms, threatening a violent cold, have gone off entirely in consequence of this plan being pursued.