540 Source of Animal Heat. the temperature of the body. Dr. Burness found that medicinal doses of morphia and strychnia raised it from 99° to `101*2°; opium and atropia raised it to 105.6°. The lowest temperature which can support life is unknown; but when the heat of the body is much lowered, all vital action is suspended, and death takes place. In some diseases, as in Asiatic cholera, the temperature of the body has been as low as 77° or 79°. Source of Animal Heat. 764. It was for a long time a received opinion among physiologists that the chief source of animal heat, was a slow kind of combustion taking place in the lungs between the oxygen of the air which enters the chest in breathing, and the carbon derived from the food, and contained in the blood circulating through the lungs. Carbonic acid and water-watery vapours-were produced and expelled in breathing, while the heat arising from this slow union of oxygen with carbon and hydrogen, was carried off by the blood and distributed throughout the body. The changes in the blood produced by breathing, are elsewhere described (see Animal Physics). It may now be stated that, besides a striking change in colour, the oxygenated blood being of a bright florid red, there is a slight difference in temperature. It contains more oxygen, less carbonic acid, and less nitrogen. According to Magnus, the quantity of oxygen contained in arterial blood, is twice as great as that in venous blood, being about ten per cent. of the volume of the former, and only five per cent. of the volume of the latter. The quantity of carbonic acid is equal to twenty per cent. by volume in the arterial, and twenty-five per cent. in the venous. These facts prove that the lungs do not act as a furnace to supply heat to the body. They are no warmer than other parts. It has been found, indeed, that the temperature of the blood in the left side of the heart, after it has traversed the whole of the lungs, is not more than one or two degrees higher than on the right side before it has been distributed through these organs. The oxygen received into the lungs penetrates the blood through the walls of the air-cells, and displaces the carbonic acid already contained in them. The oxygen is partly dissolved by the blood, and partly combined with the red colouring particles (oxygen carriers). It is thus transferred to the capillary system of vessels, and brought in contact with the waste elements of the tissues, which are fit for Its Production by Oxidation. 541 oxidation and removal from the body. It is estimated that one half of the oxygen thus disappears from the arterial blood, while an equivalent quantity of carbonic acid and water is formed. The arterial is thus changed into venous blood all over the body, and the heat given out in this constant production of carbonic acid and water is distributed over a very wide area. The venous blood, containing carbonic acid, thus collected from the waste structures throughout all parts of the body, is carried to the lungs, where a portion of it is thrown off, and its place supplied by a great portion of oxygen. 765. From certain chemical properties possessed by the red colouring particles of blood, there is reason to believe that a part of the oxygen received into the lungs, passes into the blood in the state of ozone-a condition in which it is best adapted for ready combination with hydrogen and carbon. The oxidation-changes, therefore, by which heat is maintained in a living animal, instead of being confined to the lungs, are actually taking place over the whole of the body. The circulating oxygen combines with the carbon and hydrogen of the wasted tissues, and in this process of oxidation, as much heat is given out, as under ordinary combustion, although it is much more slowly evolved, the amount of heat depending on the quantity of material oxidized. Attempts have been made to determine the quantity of carbon and hydrogen daily expelled from the lungs, based on the increase of carbonic acid and aqueous vapour contained in the expired air. As to the carbon, assuming that the expired air contains only three per cent. of carbonic acid (the lowest), and that 540 cubic inches of air are expired in one minute, it would follow that this would contain 16 cubic inches of carbonic acid, weighing 752 grains = 2 grains of solid carbon. This would be equivalent to 6 ounces of carbon or solid charcoal eliminated from the body by the lungs daily; but it is probable that the actual quantity is greater than this. Expired air, according to circumstances, may contain from three to ten per cent. Assuming an average of six per cent. the quantity of carbon oxidized and thrown out from the lungs in twenty-four hours, would be equivalent to 12 ounces of charcoal! The quantity of water representing the hydrogen of the waste tissues, as well as the vapour of the blood expelled from the lungs in twenty-four hours, has been estimated at from 6 to 27 ounces. In combining with hydrogen, oxygen evolves nearly three times as much heat as in combining with carbon. From the slow oxidation of these two elements, animal heat is chiefly derived. 542 Warmth necessary to Life. This heat-producing pcwer is eminently under the control of the nervous system. 766. It has been stated that when a person dies, the body gradually cools until it has fallen in all parts, to the temperature of the room in which it is placed. There is, probably, no more certain sign of real death than this, although some remarkable exceptions have been noticed. In some fatal cases of Asiatic cholera, although the bodies had in the first instance cooled, the temperature subsequently rose to 87° and 92°. In some fatal diseases of the brain the temperature of the body has risen after death from 104° to 111°. In a fatal case of small-pox, Mr. Simon states that after death the temperature rose to 104° and 113°. Other observers have met with similar instances of a much higher temperature appearing after death, than was observed in the body just before death. It is difficult to explain these facts. No physical cause could be assigned for them. As breathing had for some time entirely ceased, they could not be assigned to any circulation through the lungs. But by the stoppage of the heart's action, circulation had ceased throughout the body. Certain chemical changes were probably still going on in the capillary system sufficient to account for the production of heat. Artificial Climate producible by the arts of warming and ventilating. 767. The four essentials to the life and health of human beings are pure air, warmth, aliment, and rest, alternating with action. An individual if deprived of the first, dies in a few minutes, as by drowning or any other form of suffocation; if deprived of the second, he dies in a few hours, as when overwhelmed in a snow-storm; if deprived of the third, he dies in a few days, as when left on a bare rock after shipwreck; and if deprived of the fourth, he dies in a few days, weeks, or months, according to other circumstances. Want or faulty management in regard to the first two of these, are the chief causes of much of the imperfect health and the premature mortality suffered by the inhabitants of changeable climates. Human beings living in the savage state without houses, use fire principally for the purpose of cooking food, the fuel being wood burning on the ground in the open air. A very small portion of the heat so produced, is turned to account, the gross amount being dissipated into space, partly by radiation and partly by being carried away in combination with the smoke. Warming of Dwellings. 543 Of fire burning in an enclosed space, all the heat is retained, giving warmth to the substance of the walls and to the air within them. It would have been, therefore, a very simple affair in cold weather to warm a closed apartment to any desired degree by lighting a fire in it, but for the fact that the smoke and other products of combustion are destructive to life.* When the object was, therefore, to warm the air in any dwelling by a fire, it was found necessary to have an opening in the roof or ceiling by which the smoke might escape; or the fire had to be made in an enclosed space beneath the floor, through which the heat would slowly penetrate by conduction; or it might burn in a close receptacle in the room, to be called a stove, constructed of brick or other material, and having a channel for smoke leading directly to the outer atmosphere. In England, up to a late time, it was common in spacious halls, as of colleges, courts of law, and elsewhere, to have a great brazier or hearth near the middle or at one end of the room, with an opening for smoke above. 768. It was an important advance in the art of warming rooms by open fires, when the fuel was placed against the wall to radiate around, and a chimney-flue was constructed in the wall over it to carry away the smoke without allowing any mixture with the air of the room. The arrangement of the fireplace and chimney in the wall had become general in this kingdom in the last century. In countries where the winters are colder than in England, as in the northern continental parts of Europe, it is found that sittingrooms cannot be satisfactorily warmed by open fires of any magnitude, because of the loss of heat through the wide chimney, and as * Although it is now generally known that for the healthy performance of respiration, we require a regulated supply of pure air and the simultaneous removal of that which has been vitiated by combustion, there are many educated persons who warm their dwellings by stoves in which gas or charcoal is burnt, without any provision for carrying off the products. Under our patent laws, stoves on this principle have been allowed to be patented for general use, and the public have been led to believe that what is called patent fuel (charcoal) can be burnt, and give out heat without removing oxygen and substituting the injurious carbonic acid. A proper Sanitary Board would not allow such dangerous methods of warming to be made the subject of a patent. One of two results must follow. Either the stove gives out no heat, and is therefore useless, or in proportion to its evolving heat, it vitiates the air, and renders it unfit for breathing. 544 The Open Fire-grate. a consequence, close stoves of masonry or of metal are universally used, as well in royal palaces as in the dwellings of the poor, not from the motive of saving fuel, but for the sake of comfort and health. 769. At the beginning of this century, Benjamin Thompson, more commonly known as Count Rumford, while engaged with other philanthropists in establishing the Royal Institution of London, in which, since then, Davy, Faraday, and other distinguished men have laboured so usefully for the public good, proved that in the common open English fireplace more than seven-eighths of the heat produced, was carried away with the smoke to waste; and he ascertained and taught that the single change of narrowing considerably the throat of the chimney would save nearly half the fuel.* Innumerable projects for further improvement have since then been offered, for which patents have been taken, mostly, however, by persons who had little scientific knowledge on the subject, but none of them have been accepted, like Rumford's, as generally useful. The writer has noticed this subject in a short treatise adapted for popular instruction, and has suggested certain remedies. 770. THE OPEN FIRE-GRATE.-The grate is a cage or receptacle for fuel, about ten inches deep, fourteen inches broad, and nine or ten inches from back to front. It has usually two or three bars of iron in front, the sides and back are of iron or fire-brick, and the bottom is an iron grating allowing air to enter and ashes to fall out. There is left a large open space between the fire and the smoke-flue above, causing much of the waste. To prepare for lighting, the grate is charged with common bituminous coal, having firewood and paper beneath. When the paper is lighted, combustion gradually spreads, causing much smoke and tarry vapour to arise, part of which is deposited in the flue as soot. Slight causes may send part of the smoke back into the room. The fuel being consumed rapidly, requires frequent renewal, and hence constant attention and poking are necessary to obtain any approach to uniformity of action. Strong currents of cold air flow from the doors and windows towards the chimney, and without this the heated smoke and vapour would not ascend. A great aim in regard to such open fires has been to lessen the formation of smoke. The writer saw that much good might be * According to Faraday an ordinary fire consumes in twelve hours forty pounds of coal, and this, by combustion, spoils 42,000 gallons of air, and causes at the same time to pass up the chimney 200,000 gallons of air. |