PRESERVATION OF HEALTH. A HUMAN will continue in health HUMAN being, supposing him to be soundly | epidemics. A noted instance of its thus acting till he reaches old age, provided that certain conditions are observed, and no injurious accident shall befall. This is a proposition so well supported by extensive observation of facts, that it may be regarded as an established maxim. It becomes, therefore, important to ascertain what are the conditions essential to health, that, by their observance, we may preserve for ourselves what is justly esteemed as the greatest of earthly blessings, and dwell for our naturally appointed time upon the earth. A general acquaintance with these conditions may be easily attained by all, and to render them obedience is much more within the power of individuals than is commonly supposed. The leading conditions essential to health are1. A constant supply of pure air; 2. A sufficiency of nourishing food, rightly taken; 3. Cleanliness; 4. A sufficiency of exercise to the various organs of the system; 5. A proper temperature; 6. A sufficiency of cheerful and innocent enjoyments; | and, 7. Exemption from harassing cares. These conditions we shall now treat in succession, taking as our guides the most recent and eminent of physiological authorities. AIR. The common air is a fluid composed mainly of two gases, in certain proportions-namely, 20 parts of oxygen and 80 of nitrogen in 100, with a very minute addition of carbonic acid gas. (See CHEMISTRY.) Such is air in its pure and normal state, and such is the state in which we require it for respiration. When it is loaded with any admixture of a different kind, or its natural proportions are in anyway deranged, it cannot be breathed without producing injurious results. We also require what is apt to appear a large quantity of this element of healthy existence. The lungs of a healthy full-grown man will inhale the bulk of twenty cubic inches at every inspiration, and he will use no less than fifty-seven hogsheads in twenty-four hours. And not only is this large quantity necessary, but the air that surrounds us must be in free circulation, in order that what we expire may be speedily carried away, and allowed to commingle with the atmosphere, which is subject to never-ceasing causes tending to its restoration and renewal. Now, there are various circumstances which tend to surround us at times with vitiated air, and which must accordingly be guarded against. That first calling for attention is the miasma or noxious quality imparted to the atmosphere in certain districts by stagnant water and decaying vegetable matter. It is now generally acknowledged that this noxious quality is, in reality, a subtile poison, which acts on the human system through the medium of the lungs, producing fevers and other on a great scale is presented in the Campagna di Roma, where a large surface is retained in a marshy state. The exhalations arising from that territory at certain seasons of the year, oblige the inhabitants of the adjacent districts to desert their homes, and escape their pernicious influence. All marshes, and low damp grounds of every kind, produce more or less miasma; and it is consequently dangerous to live upon or near them. Slightly elevated ground, with a free exposure to light and air, should, accordingly, in all cases be chosen for the sites of both single houses and towns. Tanks and collections of water of every kind are dangerous beneath or near a house, because, unless their contents be constantly in a state of change, which is rarely the case, their tendency is to send up exhalations of a noxious kind. Some years ago, Viscount Milton-a youth of great promise, and who had recently become a husband and father-died of a fever which was traced to the opening of an old reservoir of water underneath the country-house in which he dwelt. A similar, but more extensively fatal tragedy took place at a farmhouse in the south of Scotland. Not only did the farmer, his wife, and a female servant sink under a malignant fever, but a son and daughter, and several other servants, narrowly escaped with their lives, and only by removing from the house. It was observed in this case that removal produced instantaneous improvement of health, but a return to the devoted dwelling at once renewed the ailment. On proper investigation, it was found that immediately behind the house was a kind of millpond, into which every kind of refuse was thrown, or allowed to discharge itself; and that this collection of putrid matter had not been once cleared out for a long series of years, no one dreaming of any harm from it. The momentous consequences from a cause so trifling, and the consideration that they might have been warded off by only a little knowledge of natural causes, furnish melancholy matter for reflection. Many analogous cases, which might be referred to, demonstrate that we are yet but in the infancy of an understanding of the subject of aërial poisons. Putrid matter of all kinds is another conspicuous source of noxious effluvia. The filth collected in ill-regulated towns-ill-managed drains - collections of decaying animal substances placed too near or within private dwellings-are notable for their effects in vitiating the atmosphere and generating disease in those exposed to them. In this case also it is a poison, diffused abroad through the air, which acts so injuriously on the human frame. This was probably the main cause of the plagues which devastated European cities during the middle ages. In those days there were no adequate provisions for public cleaning, and the consequence was, that masses of filth were suffered to accumulate. The noxious air diffused by these means through the narrow streets and confined dwellings would tend to the most fatal effects. In old drains there is generated a gas-sulphuretted hydrogen-which is calculated to produce dreadful consequences in those exposed to its inhalation. It has lately been discovered that it is the presence of this gas, arising from the shores, river deltas, and mangrove jungle of tropical Africa, which causes the peculiar unhealthiness of that region. It is ascertained that small animals, such as birds, die when the air they breathe contains one-fifteen-hundredth part of sulphuretted hydrogen, and that an infusion six times greater will kill a horse. It follows that we can scarcely attach too much importance to measures for cleaning and improving the sewerage of cities. There are as yet no large towns in Britain kept in a state so clean as is desirable for the welfare of their inhabitants; nor will they be so till the measures now in agitation for improved modes of construction, for adequate supplies of pure water, and for thorough scavengering and sewerage, be adopted. The human subject tends to vitiate the atmosphere for itself, by the effect which it produces on the air which is breathed. Our breath, when we draw it in, consists of the ingredients formerly mentioned, but it is in a very different state when we part with it.. On passing into our lungs, the oxygen, forming the lesser ingredient, enters into combination with the carbon of the venous blood -or blood which has already performed its round through the body in this process about two-fifths of the oxygen is abstracted and sent into the blood, only the remaining three-fifths being expired along with the nitrogen nearly as it was before. In place of the oxygen consumed, there is expired an equal volume of carbonic acid gas, such gas being a result of the process of combination just alluded to. Now, carbonic acid gas in a larger proportion than that in which it is found in the atmosphere, is noxious. The volume of it expired by the lungs, if free to mingle with the air at large, will do no harm; but if breathed out into a close room, it will render the air unfit for being again breathed. Suppose an individual to be shut up in an air-tight box; each breath he emits throws a certain quantity of carbonic acid gas into the air filling the box; the air is thus vitiated, and every successive inspiration is composed of worse and worse materials, till at length the oxygen is so much exhausted that it is insufficient for the support of life. He would then be sensible of a great difficulty in breathing, and in a little time longer he would die. Most rooms in which human beings live are not strictly close. The chimney and the chinks of the door and windows generally allow of a communication to a certain extent with the outer air, so that it rarely happens that great immediate inconvenience is experienced in ordinary apartments from want of fresh air. But it is at the same time quite certain that in all ordinary apartments where human beings are assembled, the air unavoidably becomes considerably vitiated; for in such a situation there cannot be a sufficiently ready or copious supply of oxygen to make up for that which has been consumed-the carbonic acid gas will be constantly accumulating, and there is also putrefying organic matter in the vapour of the breath. This is particularly the case in bed-chambers, and in theatres, assembly-rooms, churches, and schools. An extreme case was that of the celebrated Black Hole of Calcutta, where 146 persons were confined for a night in a room eighteen feet square with two small windows. Here the oxygen, scarcely sufficient for the healthy supply of one person, was called upon to support a large number. The unfortunate prisoners found themselves in a state of unheard-of suffering; and in the morning all were dead but twenty-three, some of whom afterwards sunk under putrid fever, brought on by breathing so long a tainted atmosphere. Although the vitiation of the air in ordinary apartments and places of public assembly does not generally excite much attention, it nevertheless exercises a certain unfavourable influence on health in all the degrees in which it exists. Perhaps it is in bedrooms that most harm is done. These are generally smaller than other rooms, and they are usually kept close during the whole night. The result of sleeping in such a room is very injurious. A common fire, from the draught which it produces, is very serviceable in ventilating rooms, but it is at best a defective means of doing so. The draught which it creates generally sweeps along near the floor between the door and the fire, leaving all above the level of the chimney-piece unpurified. Yet scarcely any other arrangement is anywhere made for the purpose of changing the air in ordinary apartments. To open the window is a plan occasionally resorted to, but it is not always agreeable in our climate, and sometimes it produces bad consequences of a different kind. A plan, to a considerable extent serviceable, though not perfect, for producing a draught from a room possessing a fire-place, was suggested by the philanthropic Dr Arnott. It is only necessary to make an aperture into the flue, near the ceiling of the room, and insert therein a tin tube, with a valve at the exterior, capable of opening inwards, but closing when at rest, or when a draught is sent the contrary way. The draught produced by the fire in the flue causes a constant flow of air out of the upper part of the room (where most vitiated); and the valve is a more or less effectual protection against back-smoke. This plan can be applied to any existing house at a mere trifle of expense. (For various modes of ventilation, see No. 31.) FOOD. The second requisite for the preservation of health is a sufficiency of nutritious food. Organic bodies are constituted as explained under PHYSIOLOGY-upon the principle of a continual waste of substance supplied by continual nutrition. The nutritive system of animals, with the exception of the very lowest animal organisms (see ZOOLOGY, vol. i. 129), comprehends an alimentary tube or cavity, into which food is received, and from which, after undergoing certain changes, it is diffused by means of smaller vessels throughout the whole structure. In the form of this tube, and in the other apparatus connected with the taking of food, there are in different animals varieties of structure, all of which are respectively in conformity with peculiarities in the quality and amount of food which the particular animals are designed to take. Man designed to live on a Mixed Diet. The followers of Pythagoras argued, from the cruelty of putting animals to death, that it was proper to live on vegetables alone; and eccentric persons of modern times have acted upon this rule. But the ordinances of Nature speak a different language; and if we have any faith in these, we cannot for a moment doubt that a mixture of animal food is necessary for our well-being. On the other hand, we cannot dispense with vegetable food without injurious consequences. In that case, we place in a medium alimentary canal a kind of food which is calculated for a short one, thus violating an arrangement of the most important nature. A balance between the two kinds of food is what we should observe, if we would desire to live a natural and healthy life. Rules connected with Eating. In order fully to understand how to eat, what to eat, and how to conduct ourselves after eating, it is necessary that we should be acquainted in some measure with the process of nutrition-that curious series of operations by which food is received and assimilated by our system, in order to make good the deficiency produced by waste. Even in the introductory stage there are certain rules to be observed. Strange as it may appear, to know how to eat is physiologically a matter of very considerable importance. Many persons, thinking it all a matter of indifference, or perhaps unduly anxious to despatch their meals, eat very fast. If we are to believe the accounts of travellers, the whole of the mercantile classes in the United States of America eat hurriedly, seldom taking more than ten minutes to breakfast, and a quarter of an hour to dinner. They tumble their meat precipitately into their mouths, and swallow it almost without mastication. This is contrary to an express law of nature, as may be very easily demonstrated. Food, on being received into the mouth, has two processes to undergo, both very necessary to digestion: it has to be masticated, or chewed down, and also to receive an admixture of saliva. The saliva is a fluid arising from certain glands in and near the mouth, and approaching in character to the gastric juice afterwards to be described. Unless food be well broken down or masticated, and also well mixed up with the salivary fluid, it will be difficult of digestion. The stomach is then called upon to perform, besides its own proper function, that which properly belongs to the teeth and saliva, and it is thus overburdened, often to a very serious extent. The pains of indigestion are the immediate consequence, and more remote injuries are likely to follow. The importance of the saliva has been shewn in a striking manner on several occasions when food was received into the stomach otherwise than through the mouth. A gentleman, who, in consequence of a stricture in the gullet, had his food introduced by an aperture into that tube, used to suffer severely from indigestion. It is recorded of a criminal, who, having cut his throat in prison without fatal consequences, required to get his food introduced by means of a tube inserted by the mouth, that every time he was fed there was an effusion of saliva to the amount of from six to eight ounces, We cannot suppose that a fluid of a peculiar character would have been prepared in such quantity, when water would serve as well merely to moisten the food, if it had not been designed to act an important part in the business of nutrition. With regard to mastication, the evidence of its importance is still more decided. Some years ago, a young Canadian, named Alexis St Martin, had a hole made by a shot into his stomach, which healed without becoming closed. It was therefore possible to observe the whole operations of the stomach with the eye. His medical attendant, Dr Beaumont, by these means ascertained that when a piece of solid food was introduced, the gastric juice acted merely on its outside. It was only when the food was comminuted, or made small, that this fluid could fully perform its function. When the stomach finds itself totally unable to digest a solid piece of food, it either rejects it by vomiting, or passes it on into the gut, where it produces an irritating effect, and is apt to occasion an attack of colic or flatulency. It must therefore be concluded, that a deliberate mastication of our food is conducive to health, and that fast eating is injurious, and sometimes even dangerous. The food, having been properly masticated, is by the action of the tongue thrown into the gullet. It then descends into the stomach, not so much by its own gravity, as by its being urged along by the_contractions and motions of the gullet itself. The stomach may be considered as an expansion of the gullet, and the chief part of the alimentary canal. It is, in fact, a membranous pouch or bag, very similar in shape to a bagpipe, having two openings, the one by which the food is admitted, the other that by which it is passed onward. It is into the greater curvature of the bag that the gullet enters; at the lesser, it opens into that adjoining portion of the canal into which the half-digested mass is next propelled. When food has been introduced, the two orifices close, and that which we may term the second stage in the process of digestion commences. The mass, already saturated with saliva, and so broken down as to expose all its particles to the action of the gastric juice, is now submitted to the action of that fluid, which, during digestion, is freely secreted by the vessels of the stomach. The most remarkable quality of this juice is its solvent power, which is prodigious. The food exposed to this dissolving agency is converted into a soft, gray, pulpy mass, called chyme, which, by the muscular contraction of the stomach, is urged on into the adjoining part of the alimentary canal, called the duodenum. This is generally completed in the space of from half an hour to two or three hours; the period varying according to the nature and volume of the food taken, and the degree of mastication and insalivation it has undergone. In the duodenum, the chyme becomes intimately mixed and incorporated with the bile and pancreatic juices; also with a fluid secreted by the mucous follicles of the intestine itself. The bile is a greenish, bitter, and somewhat viscid fluid, secreted by the liver, which occupies a considerable space on the right side of the body immediately under the ribs. From this organ the bile, after a portion of it has passed up into the adjacent gall-bladder, which serves as a reservoir, descends through a small duct, about the size of a goose-quill, into the duodenum. The chyme, | exercise of any kind. Both body and mind are when mixed with these fluids, undergoes a change inactive and languid. They are so simply because in its appearance: it assumes a yellow colour and that which supports muscular and mental activity bitter taste, owing to the predominance of the is concentrated for the time upon the organs of bile in the mass; but its character varies accord-digestion. ing to the nature of the food that has been taken. Fatty matters, tendons, cartilages, white of eggs, &c. are not so readily converted into chyme as fibrous or fleshy, cheesy, and gelatinous substances. The chyme, having undergone the changes adverted to, is urged by the peristaltic motion of the intestines onwards through the alimentary canal. This curious motion of the intestines is caused by the contraction of the muscular coat which enters into their structure, and one of the principal uses ascribed to the bile is that of stimulating them to this motion. If the peristaltic motion be diminished, owing to a deficiency of bile, then the progress of digestion is retarded, and the intestines become constipated. In such cases, calomel, the blue pill, and other medicines, are administered, for the purpose of stimulating the liver to secrete the biliary fluid, that it may quicken, by its stimulating properties, the peristaltic action. The preceding, however, is not the only use of the bile; it also assists in separating the nutritious from the non-nutritious portion of the alimentary mass, for the chyme now presents a mixture of a fluid termed chyle, which is in reality the nutritious portion eliminated from the food. The chyme thus mixed with chyle arrives in the small intestines, on the walls of which a series of exquisitely delicate vessels ramify in every direction. These vessels absorb or take up the chyle, leaving the rest of the mass to be ejected from the body. The chyle, thus taken up, is carried into little bodies or glands, where it is still further elaborated, acquiring additional nutritious properties; after which corresponding vessels, emerging from these glands, carry along the fluid to a comparatively large vessel, called the thoracic duct, which ascends in the abdomen along the side of the backbone, and pours it into that side of the heart to which the blood that has already circulated through the body returns. Here the chyle is intimately mixed with the blood, which fluid is now propelled into the lungs, where it undergoes, from being exposed to the action of the air we breathe, the changes necessary to render it again fit for circulation. It is in the lungs, therefore, that the process of digestion is completed the blood has now acquired those nutritive properties from which it secretes the new particles of matter adapted to supply the waste of the different textures of the body. When food is received into the stomach, the secretion of the gastric juice immediately commences; and when a full meal has been taken, this secretion generally lasts for about an hour. It is a law of vital action, that when any living organ is called into play, there is immediately an increased flow of blood and nervous energy towards it. The stomach, while secreting the gastric juice, displays this phenomenon, and the consequence is that the blood and nervous energy are called away from other organs. This is the cause of that chilliness at the extremities which we often feel after eating heartily. So great is the demand which the stomach thus makes upon the rest of the system, that during and for some time after a meal we are not in a condition to take strong This is an arrangement of nature which a regard to health requires that we should not interfere with. We should indulge in the muscular and mental repose which is demanded; and this should last for not much less than an hour after every regular meal. In that time the secretion of gastric juice is nearly finished, and we are again fit for active exertion. The consequence of not observing this rule is often very hurtful. Strong exercise, or mental application, during or immediately after a meal, diverts the flow of nervous energy and of blood to the stomach, and the process of digestion is necessarily retarded or stopped. Confusion and obstruction are thus introduced into the system, and a tendency to the terrible calamity of dyspepsy is perhaps established. For the same reason that repose is required after a meal, it is necessary in some measure for a little while before. At the moment when we have concluded a severe muscular task—such, for example, as a long walk-the flow of nervous energy and of circulation is strongly directed to the muscular system. It requires some time to allow this flow to stop and subside; and till this takes place, it is not proper to bring the stomach into exercise, as the demand which it makes when filled would not in that case be answered. In like manner also, if we be engaged in close mental application, the nervous energy and circulation being in that case directed to the brain, it is not right all at once to call another and distant organ into play; some time is required to allow of the energy and circulation being prepared to take the new direction. It may therefore be laid down as a maxim, that a short period of repose, or at least of very light occupation, should be allowed before every meal. It is remarkable that these rules, although the natural reasons for them were not perhaps well known, have long been followed with regard to animals upon which man sets a value, while as yet their application to the human constitution is thought of only by a few. Those intrusted with horses and dogs will not allow them to feed immediately after exercise; nor will they allow them to be subjected to exercise for some time after feeding. Experience has also instructed veteran soldiers not to dine the instant that a long march has been concluded, but to wait coolly till ample time has been allowed for all the proper preparations. Although strong mental and muscular exercise should be avoided before, during, and immediately after a meal, there can be no objection to the light and lively chat which is generally indulged in where several are met to eat together. On the contrary, it is believed that jocund conversation is useful towards the process of nutrition. Kinds of Food. It has been shewn, by a reference to the structure of the human intestinal canal, that our food is designed to be a mixture of animal and vegetable substances. There is, it is to be remarked, a power of adaptation in nature, by which individuals may be enabled for a considerable time to human constitution. They generally require under two hours for digestion, or about half the time of a full mixed meal. The cottage children of Scotland, reared exclusively upon oaten porridge and bread, with potatoes and milk, may be cited as a remarkable example of a class of human beings possessing in an uncommon degree the blessing of health. One important consideration here occurs: there is need for a certain bulk in our ordinary food. Receiving nutriment in a condensed form, and in a small space, will not serve the purpose. This is because the organs of digestion are calculated for receiving our food nearly in the condition in which nature presents it—namely, in a considerable bulk with regard to the proportion of its nutritious properties. The same law applies with respect to the lower animals. When a horse is fed upon corn alone, it does not thrive. The present writer is much inclined to doubt the propriety of grinding off the coarse exterior of wheaten grain. It does not seem by any means likely that nature calculated the human aliment live healthily on one or the other kind exclusively, or nearly so. The above is, nevertheless, the general rule, to which it is safest to adhere. It has been found, for instance, that field-labourers, including ploughmen, will live healthily for many years on a diet chiefly farinaceous-that is, composed of the farina of grain. But it is to be feared that the food in this case, though apparently sufficient for health, is only so apparently; and that the constitution, being all the time not supported as it ought to be, breaks down prematurely in a great proportion of instances. It has been said, again, that the Irish labouring-classes are a remarkably robust race, although their food consists almost exclusively of potatoes. The fact is overlooked, that the Irish eat a quantity of potatoes so enormous as could not fail to make up in some measure for the want of animal diet. It was found by the Poor-law Commissioners, that the greater number of the peasantry of Ireland, women as well as men, take at their two daily meals in general about nine pound-weight of this aliment! Such a case is rather to be ranked amongst instances of extra-ary cavity for the use of the white interior of the ordinary adaptations to a particular variety of food, than as a proof that an unmixed potato-diet is healthy. Climate has a remarkable effect in modifying the rule as to the mixture and amount of animal and vegetable food. The former has most of a stimulating quality, and this quality is greater in beef, and flesh in general, than in fowl or fish. Now, the inhabitants of torrid countries are, in their ordinary condition, least in need of stimulus; hence they find a simple diet of rice and sago sufficient for them. Those, on the contrary, who dwell in cold countries need much stimulus; hence they can devour vast quantities of flesh and blubber, with scarcely any mixture of vegetable food. Inquiries with respect to the comparative digestibility of different kinds of food are perhaps chiefly of consequence to those in whom health has already been lost. To the sound and healthy, it is comparatively of little consequence what kind of food is taken, provided that some variation is observed, and no excess committed as to quantity. Within the range of fish, flesh, and fowl, there is ample scope for a safe choice. There is scarcely any of the familiar aliments of these kinds but, if plainly dressed, will digest in from two to four hours, and prove perfectly healthy. One rule alone has been pretty well ascertained with respect to animal foods, that they are the more digestible the more minute and tender the fibre may be. They contain more nutriment in a given bulk than vegetable matters, and hence their less need for length of intestine to digest them. Yet it is worthy of notice, that between the chyle produced from animal and that from vegetable food no essential distinction can be observed. Tendon, suet, and oily matters in general, are considerably less digestible than the ordinary fibre; and these are aliments which should be taken sparingly. Pickling, from its effect in hardening the fibre, diminishes the digestibility of meat. Dressed shell-fish, cheese, and some other animal foods are avoided by many as not sufficiently digestible. Farinaceous foods of all kinds-wheat, oaten, and barley bread, oaten porridge, sago, arrow-root, tapioca, and potatoes-are highly suitable to the grain, exclusive of all the rest, which consists of very different but not less necessary chemical constituents. Wheat forms so large a part of our daily food, that if this be the case, we unquestionably make a departure of a very important kind from the laws of health. Experience is favourable to this view, for the effect of coarse brown bread in relaxing, seems only comparable to that of white bread in constipating the bowels. Quantity of Food-Number and Times of Meals. With respect to the amount of food necessary for health, it is difficult to lay down any rule, as different quantities are safe with different individuals, according to their sex, age, activity of life, and some other conditions. There is a general and probably well-founded opinion, that most persons who have the means eat too much, and thereby injure their health. This may be true, and yet it may not be easy to assign to such persons a limit beyond which they ought not to go. The best authorities are obliged to refer the matter to our own sensations. Dr Beaumont, for example, says that we should not eat till the mind has a sense of satiety, for appetite may exceed the power of digestion, and generally does so, particularly in invalids; but to a point previous to that, which may be known by the pleasurable sensations of perfect satisfaction, ease, and quiescence of body and mind. The number and times of meals are other questions as yet undetermined. As the digestion of a meal rarely requires more than four hours, and the waking part of a day is about sixteen, it seems unavoidable that at least three meals be taken, though it may be proper that one, if not two of these, be comparatively of a light nature. Breakfast, dinner, and tea as a light meal, may be considered as a safe, if not a very accurate prescription for the daily food of a healthy person. Certainly four good meals a day is too much. No experiments, as far as we are aware, have been made with regard to the total amount of solids which a healthy person in active life may safely take in a day. It has been found, however, that confined criminals and paupers are healthiest when the daily solids are not much either above or below twenty-five ounces. Of course, in active life |