Mr. Hutchinson has found that two other conditions of the body besides the height, regulate the quantity of air that passes to and from the lungs in forced voluntary respi ration, and these are age and weight. He states that weight does not affect the respira tory power of an individual of any height between 5 feet I inch and 5 feet 11 inches until it has increased 7 per cent. above the average weight of the body in persons of that height, but beyond this it diminishes in the relation of 1 cubic inch per pound for the next 35 pounds—the limit of the calculation. In males of the same height the respiratory power is increased from 15 up to 35 3ears of age, but from 35 to 65 years it decreases nearly 11. cubic inch for each year.t Bourgery concludes from his experiments already re ferred to, that the measure of l'espiration (by which he apparently means the quantity of air which may be drawn into the lungs by a forced inspiration) is greater the younger and thinner the person is ; that its maximum in both sexes occurs at the age of 30; that the relation of a forced and ordinary respiration diminishes with the age of the individual, being, he says, from 1 to 12 at three years of age, as 1 to 10 at fifteen, as 1 to 9 at twenty, as 1 to 3 at sixty, and as 1 to or at eighty years; .whence it follows that in youth there is an immense respiratory power in reserve for any violent exertion, while in old age the individual tinder such circumstances is at once out of breath.* Changes upon the atmospheric air in respi of the most obvious changes, under ordinary circumstances, upon the air that enters the lungs in respiration is an increase of its temperature, and consequently an augmentation of its bulk. As a quantity of water is readily supplied by the fluid secre tions of the inner surface of the air-passages, and by the blood in the pulmonary capillaxy blood-vessels, this augmentation of the tem perature of the air is also necessarily attended by an increase of its watery vapour, and con sequently by an additional increase in its bulk and elasticity. The expired air, therefore, contains more caloric, more watery vapour, is more elastic, and is of less specific gravity than the inspired air. Valentin performed 12 experiments on his own person by breathing through an apparatus invented by Brunner and himself, to ascertain the temperature of the expired air, and he obtained the following results. In breathing atmospheric air of a temperature varying from 8°.5 to 33°.5 Reau mur (51°125 to 107°.375 Fah.), he observed a difference of 1°15 R. (3°.937 F.) in the temperature of the expired air. While breath ing in the lowest temperature, viz. 51°1 25 F., the temperature:of the expired air was 96°. 687 F., and was warmer than the inspired air by 45'3'562 F. ; and when breathing in the highest temperature the expired was colder than the inspired air by 6°15 F. In the last experiment, though the inspired air was 7'875 F. warmer than the internal tempera ture of the body, the expired air was only about 10'125 F. warmer than what it is when air of the ordinary temperature is breathed. The average temperature of the expired air is, according to Valentin, 99°-.5 F. when breath ing in an atmosphere of moderate tempera ture.* According to his calculations, when a person breathes 100 cubic centimeters of atmospheric air at the temperature of 60° F., their bulk is increased to 107-87975 cubic centimeters when raised to the temperature of 99-5 F. in the lungs, since the expansive co-efficient of atmospheric air is 0-3665. As the expired air, however, contains 4-4 per cent. of carbonic acid gas, and as the ex pansive co-efficient of this last gas is 0-369087 the expansion of the expired air will differ slightly from what it would be were it com posed of oxygen and nitrogen only, and will be 107-882197 cubic centimeters.t It is difficult to obtain an accurate estimate of the quantity of watery vapour that escapes front the body along with the expired air. Were the inspired and expired air always fully saturated with moisture, and were their quan tities, barometric pressure, and relative tem perature accurately ascertained, the absolute and relative quantities of watery vapour which they contain could be calculated by certain algebraic formul. The atmospheric air which we breathe is sometimes saturated with moisture, more frequently the dew-point, or that at which the precipitation of the atino spheric moisture can occur, is considerably below the temperature of the air, and the number of thermometric degrees between the actual temperature of the air and the dew point shows the degree of dryness in the air, or in other words how much it is below the point of saturation with moisture.t The loss of watery vapour by the lungs will evi dently be regulated by the temperature of the inspired air, the quantity of watery vapour it holds in solution, the volume of air inspired, and the length of time it remains in the lungs. The lower the temperature of the inspired air, the less it approaches to the point of sa turation with moisture, and the greater its volume, the greater will be the loss of watery vapour by the lungs. When the respirations are more rapid, and the sojourn of the air within the lungs is short, the same volume of expired air will probably contain less water in solution, than when its sojourn there is more prolonged, but the more frequent renewal of the air within the lungs will be more than sufficient to compensate for this.
The most correct and trust-worthy expe riments to ascertain by the direct method the quantity of watery vapour in the expired air are those of Valentin and Brunner.* These experiments were performed upon seven males between the ages of 17L and 33 years,. and the maximum of watery vapour exhaled was 131.56-323 Troy grains in the 21 hours; the minimum 4511-374 grains, and the average 7819-222 grains. The quantity of watery vapour in the expired air within a given time varied in the same individual ; and in one experiment it was increased after drinking. In these experiments the entire quantity of water in the expired air was ascertained, so that the actual quantity given, off by the fluids of the body must have been, less than this ; and Valentin calculates that if a person breathes atmospheric air saturated with moisture, at the temperature of 60° Fahr., and if the expired air be at the temperature of 99°-.5 Fehr., and also saturated with moisture, about of the watery vapour contained in the expired air will be fUrnished by the fluids of the body.t We have seen that several of the calculations of the amount of the watery vapour exhaled from the lungs proceed on the supposition that the expired air is saturated with moisture, but this has not been substantiated by the only experiments made with the view of deter mining this. point. In Moleschott's experi ments, the amount of water held in solution varied. In five out of seven experiments the watery vapour in the expired air was appre ciably less than what is sufficient to saturate air of the same temperature, while in one experiinent it was saturated. On taking the average difference in the seven experiments performed, as much as possible under similar circumstances, between the actual quantity of moisture in the expired air, and in air of the same temperature saturated with moisture, he found that 24,20 cub. cent. 04,7.620 Eng. cub. inches) of the expired air would require a quantity of watery vapour additional to that already existing in it equal to 10 millegramtnes (.150 Eng. Troy, grains) to saturate it. From these experiments he concludes " that in the greater number of instances the expired air in man is not saturated with watery vapour, but sometimes such a saturation occurs."* Magendie observed, in experiments on dogs, that the escape of an increased quantity of watery vapour from the mouth follows the injection of water into the veins, caused, as he supposes, by the transpiration from the lungs being considerably increased.t Animal matters in quantities too minute to be subjected to analysis are also exhaled from the lungs, and escape along With the expired vapour. The condensed vapour from the lungs, when collected in a vessel, and kept for some days, putrefies, and emits an ammoniacal stnell.$ We are also often sensible of the escape of different substances, previously taken into the sto mach, along with the expired air, by their smell ; and the experiments of Nysten§, Magendie*, Tiedemann-f, and others, prove that various organic and mineral substances, when injected into the veins, escape in part by exhalation from the lungs.
If the inspired air, during its sojourn in the lungs, becomes increased in bulk from an increase in temperature and an addition of watery vapour, it suffers a small diminution from the absorption of part of its constituent gases. The older experimenters observed a diminution in the air respired, but as they experimented with imperfect apparatus, and transmitted the expired air through water which would absorb part of the carbonic acid gas, little confidence is to be placed in their results.t. There can he no doubt that a greater atnount of oxygen disappears from the inspired air than what is sufficient for the formation of' the quantity of' carbonic acid gas in the expired air, and that there is a slight diminution in the bulk of the expired air from this cause ; but we cannot speak so decidedly regarding any changes in the quan tity of the nitrogen. Provencal and Hum boldt§, in their experiments on the respi ration of fishes, and Spallanzani II, in his experiments on snails, observed an absorption of azote : while Jurine I and Nysten**, in their experiments on the human species, and Ber thollet Despretztt, Dulong§§, and Mar tignyll II, in their experiments on warm-blooded animals, and Treviranuslic in his experiments on the cold-blooded animals, observed an exhalation of azote. Dr.W. F. Edwards ***, in his experiments upon warm-blooded animals and reptiles, found that in some cases the quantity of azote in the air respired was increased, in others diminished, while in others it remained unchanged ; but these changes in the quantity of azote did not equal the difference between the amount of oxygen absorbed and of carbonic acid exhaled. La voisier and Seguin*, Allen and Pepyst, Va lentin and Brunner t, and Dr. Thomson§, in their experiments on the respiration in the human species, detected no change upon the quantity of azote.11 Boussingault`f, by a series of comparative analyses of the aliments consumed, and of the excrements in a turtle dove, arrived at the conclusion by this in direct method of research that azote was exhaled.