HE leading conditions essential to health may be thus enumerated:-1. 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 right temperature; 6. A sufficiency of cheerful and innocent enjoyments; and, 7. Exemption from harassing cares.

AIR.

The common air is a fluid composed mainly of two gases, in certain proportions; namely, oxygen as twenty and nitrogen as eighty parts in a hundred, with a very minute addition of carbonic acid gas. Such is air in its pure and right 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 any way 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.

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 air in certain districts by stagnant water and decaying vegetable matter. It is now generally acknowledged that this noxious quality is in reality a subtle poison, which acts on the human system through the medium of the lungs, producing fevers and other epidemics.

Putrid matter of all kinds is another conspicuous source of noxious effluvia. The filth collected in ill-regulated townsill-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.

The human subject tends to vitiate the atmosphere for itself, by the effect which it produces on the air which it breathes.

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 vol. ume 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 urfit 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 doors 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, and the carbonic acid gas will be constantly accumulating. This is particularly the case in bedrooms, and in theaters, churches, and schools.

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 rooms.

FOOD.

The second requisite for the preservation of health is a sufficiency of nutritious food.

Organic bodies, in which are included vegetables as well as animals, are constituted upon the principle of a continual waste of substance supplied by continual nutrition.

The Nutritive System of animals, from apparently the humblest of these to the highest, 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. The armony to be observed in these arrangements is remarkably significant of that Creative design to be traced in all things.

Man Designed to Live on a Mixed Diet.-Some animals are formed to live upon vegetable substances alone; others are calculated to live upon the flesh of other animals. Herbivorous animals, as the former are called, have generally a long and complicated alimentary tube, because the nutritious part of such food, being comparatively small in proportion to the whole bulk, requires a greater space in which to be extracted and absorbed into the system. The sheep, for example, has a series of intestines twenty-seven times the length of its body. For the opposite reasons carnivorous or flesh-devouring animals, as the feline tribe of quadrupeds, and the rapacious birds, have generally a short intestinal canal. The former class of animals are furnished with teeth calculated by their broad and flat surfaces, as well as by the lateral movement of the jaws in which they are set, to mince down the herbage and grain eaten by them. But the carnivorous animals, with wideopening jaws, have long and sharp fangs to seize and tear their prey. These peculiarities of structure mark sufficiently the designs of nature with respect to the kinds of food required by the two different classes of animals for their support.

The human intestinal canal being of medium length, and the human teeth being a mixture of the two kinds, it necessarily follows that man was designed to eat both vegetable and animal food. As no animal can live agreeably or healthy except in conformity with the laws of its constitution, it follows that man will not thrive unless with a mixture of animal and vegetable food. The followers of Pythagoras argued, from the cruelty of putting animals to death, that it was proper to live on vegetables alone, and many 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 consequently 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.

Food is first received into the mouth, and there the operations in question may be said to commence. It is there to be chewed (or masticated), and mixed with saliva, preparatory to its being swallowed or sent into the stomach. Even in this introductory stage, there are certain rules to be observed. Strange as it may appear, to know how to eat is a matter of very considerable importance.

Many persons, thinking it all a matter of indifference, or perhaps unduly anxious to dispatch their meals, eat very fast. 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 easily shown.

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 afterward 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 do, beside its own proper duty, that which properly belongs to the teeth and saliva, and it is thus overburdened and embarrassed, often in a very serious manner. The pains of indigestion are the immediate consequence, and more remote injuries follow.

It is therefore to 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 enters, the other that by which it passes out. It is into the greater curvature of the bag that the gullet enters; it is at its lesser that 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 mastication and insalivation it has undergone.

In the duodenum, the chyme becomes intimately mixed and incorporated with the bile and pancreatic juice; 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, descends through a small duct, about the size of a goose-quill, into the duodenum. The chyme, when mixed with these fluids, undergoes a change in its ap. pearance; it assumes a yellow color and bitter taste, owing to the predominance of the bile in the mass; but its character varies according to the nature of, the food that has been taken. Fatty matters, tendons, cartilages, white of eggs, etc., are not so readily converted into chyme as fibrous or fleshy, cheesy, and glutinous substances. The chyme, having undergone the changes adverted to, is urged by the peristaltic motion of the intestines onward 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, ow. ing to a deficiency of bile, then the progress of digestion is retarded, and the body becomes 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. But this 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 of 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 back-bone, 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 diges. tion is completed; the blood has now acquired those nutrient 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 toward it. The stomach, while secreting its fluid, 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 exercise of any kind. Both body and mind are inactive and languid. They are so, simply because that which supports muscular and mental activity is concentrated for the time upon the organs of digestion. 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 meal. In that time the secretion of gastric juice is nearly finished; the new nutriment begins to tell upon the general circulation; and we are again fit for active exertion. The consequence of not observ ing this rule is very hurtful. Strong exercise, or mental appli. cation during or immediately after a meal, diverts the flow of nervous energy and of blood to the stomach, and the proc ess of digestion is necessarily retarded or stopped. Confu sion is thus introduced into the system, and a tendency to the terrible calamity of dyspepsia 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 it makes when filled would not in that case be answered. Just so 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.

Kinds of Food.-It has been shown 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.

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 fiber 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 fiber; and these are aliments which should be taken sparingly. Pickling, from its effects in hardening the fiber, 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 human constitution. They gener ally 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. Green vegetables and fruit, however softened by dressing, are less digestible, and less healthy as a diet. 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 its nutritious properties.

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.

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.

The interval between rising and breakfast ought not to be great, and no severe exercise or task-work of any kind should be undergone during this interval. There is a general prepossession to the contrary, arising probably from the feeling of freedom and lightness which most people feel at that period of the day, and which seems to them as indicating a preparedness for exertion. But this feeling, perhaps, only arises from a sense of relief from that oppression of food under which much of the rest of the day is spent. It is quite inconsistent

with all we know of the physiology of aliment, to suppose that the body is capable of much exertion when the stomach has

been for several hours quite empty. We have known many persons take long walks before breakfast, under an impression that they were doing something extremely favorable to health. Others we have known go through three hours of mental taskwork at the same period, believing that they were gaining so much time. But the only observable result was to subtract from the powers of exertion in the middle and latter part of the day. In so far as the practice was contrary to nature, it would likewise of course produce permanent injury. Only a short saunter in the open air, or a very brief application to business or task-work, can be safely indulged in before breakfast. With regard to the time for either breakfast or dinner, nothing can be said with scientific authority.

Variety of Food.-A judicious variation of food is not only useful, but important. There are, it is true, some aliments, such as bread, which cannot be varied, and which no one ever wishes to be so. But apart from one or two articles, a certain variation of rotation is much to be desired, and will prove favorable to health. There is a common prepossession respecting one dish, which is more spoken of than acted upon. In reality, there is no virtue in this practice, excepting that, if rigidly adhered to, it makes excess nearly impossible, no one being able to eat to satiety of one kind of food. There would be a benefit from both a daily variation of food and eating of more than one dish at a meal, if moderation were in both cases to be strictly observed, for the relish to be thus obtained is useful as promotive of the flow of nervous energy to the stomach, exactly in the same manner as cheerfulness is useful. The policy which would make food in any way unpleasant to the taste, is a most mistaken one; for to eat with languor, or against inclination, or with any degree of disgust, is to lose much of the benefit of eating. On the other hand, to cook dishes highly, and provoke appetite by artificial means, are equally reprehensible. Propriety lies in the mean between the

two extremes.

Beverages.-The body containing a vast amount of fluids, which are undergoing a perpetual waste, there is a necessity for an occasional supply of liquor of some kind, as well as of solid food. It remains to be considered what is required in the character or nature of this liquor, to make it serve the end consistently with the preservation of health.

When the digestion is good and the system in full vigor, the bodily energy is easily sustained by nutritious food, and "artificial stimulant only increases the wasting of the natural strength." Nearly all physicians, indeed, concur in representing ardent liquors as unfavorable to the health of the healthy, and as being in their excess highly injurious. Even the specious defense which has been set up for their use, on the ground that they would not have been given to man if they had not been designed for general use, has been shown to be ill-founded, seeing that vinous fermentation, from which they are derived, is not a healthy condition of vegetable matter, but a stage in its progress to decay. Upon the whole, there can be little doubt that these liquors are deleterious in our ordinary healthy condition; and that simple water, toast water, whey, ginger beer, or lemonade, would be preferable (the first being the most natural and the best of all), if we could only consent to deny ourselves further indulgence.