Part 3

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. 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. 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.

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.