Part 33 (1/2)

HYGIENE OF THE RESPIRATORY ORGANS.

495. For man to enjoy the highest degree of health, it is necessary that the impure ”venous” blood be properly changed. As this is effected in the lungs by the action of the air, it follows that this element, when breathed, should be pure, or contain twenty-one per cent. of oxygen to about seventy-nine per cent. of nitrogen.

496. The volume of air expelled from the lungs is somewhat less than that which is inspired. The amount of loss varies under different circ.u.mstances. An eightieth part of the volume taken into the lungs, or half a cubic inch, may be considered an average estimate.

497. _The quality and purity of the air is affected by every respiration._ 1st. The quant.i.ty of oxygen is diminished. 2d. The amount of carbonic acid is increased. 3d. A certain proportion of watery vapor is ejected from the lungs in the expired air. Of the twenty-one parts of oxygen in the inspired air, only eighteen parts are expired, while the carbonic acid and watery vapor are increased about four per cent. The quant.i.ty of nitrogen is nearly the same in the expired as in the inspired air.

_Observation._ It is now fully ascertained that while the chemical composition of the blood is essentially changed, its weight remains the same, as the carbon and hydrogen discharged are equal to the united weight of the oxygen and nitrogen absorbed.

495-546. _Give the hygiene of the respiratory organs._ 495. What is necessary that man enjoy the highest degree of health? 496. How does the volume Of expired air compare with that which was inspired? Does this loss vary, and what is an average estimate? 497. How is the purity of the air affected by respiration? How is the inhaled oxygen affected? What effect on the carbonic acid and watery vapor? On the nitrogen? What is said respecting the weight of the blood?

498. If one fourth part of the volume of air received by the lungs at one inspiration is decomposed at one ”beat” of the heart, it might be supposed that if the expired air be again received into the lungs, one half of the oxygen would be consumed, and, in a similar ratio, if re-breathed four times, all the oxygen would be consumed. But it does not follow, if the air is thus re-breathed, that the same changes will be effected in the lungs. For air that has been inspired does not part with its remaining oxygen as freely as when it contains the proper amount of this life-giving element, and thus the changes in the impure blood are not so completely effected.

_Ill.u.s.tration._ In the process of dyeing, each successive article immersed in the dye weakens it; but it does not follow that the dye each time is affected in the same degree, or that the coloring matter by repeated immersions can be wholly extracted. The same principle applies to the exchange of oxygen and carbonic acid gas in the lungs.

499. _If the inspired air is free from moisture and carbonic acid, these substances contained in the blood will be more readily imparted to it._ When the air is loaded with vapor, they are removed more slowly; but if it is saturated with moisture, no vapor will escape from the blood through the agency of the lungs. This may be ill.u.s.trated by the following experiment: Take two and a half pounds of water, add to it half a pound of common salt, (chloride of sodium,) and it will readily mix with the water; and to this solution add the same quant.i.ty of salt, and it will be dissolved more slowly. Again, add more salt, and it will remain undissolved, as the water has become saturated by the pound before dissolved.

498. Does air that is re-breathed freely impart its oxygen? Why? 499.

What is the effect on the blood when the air is free from vapor and carbonic acid? When loaded with vapor? When saturated? How is this ill.u.s.trated?

500. The principle in this experiment is a.n.a.logous to that of the union between carbonic gas and atmospheric air. Allen and Pepy showed by experiment, that air which had been once breathed, contained eight and a half per cent. of carbonic acid. They likewise showed, that no continuance of the respiration of the same air could make it take up more than ten per cent. This is the point of saturation.

_Experiment._ Sink a gla.s.s jar that has a stop-c.o.c.k, or one with a gla.s.s stopper, into a pail of water, until the air is expelled from the jar. Fill the lungs with air, and retain it in the chest a short time, and then breathe into the jar, and instantly close the stop-c.o.c.k. Close the opening of the jar that is under the water with a piece of paper laid on a plate of sufficient size to cover the opening, invert the jar, and sink into it a lighted candle. The flame will be extinguished as quickly as if put in water.[15] Remove the carbonic acid by inverting the jar, and place a lighted candle in it, and the flame will be as clear as when out of the jar.

[15] As a subst.i.tute for a jar with a stop-c.o.c.k, take a piece of lead pipe bent in the form of a siphon, and insert it in the mouth of a reversed jar. This experiment is as conclusive whether the air is inhaled once only or breathed many times.

_Observations._ 1st. It is familiarly known that a taper will not burn where carbonic acid exists in any considerable quant.i.ty, or when there is a marked deficiency of oxygen. From this originated the judicious practice of sinking a lighted candle into a well or pit before descending into it. If the flame is extinguished, respiration cannot there be maintained, and life would be sacrificed should a person venture in, until the noxious air is removed.

500. What did the experiments of Allen and Pepy show? How can the presence of carbonic gas in the expired air be demonstrated? State observation 1st. Observation 2d.

2d. It is the action of carbonic acid upon the respiratory organs, that gives rise to a phenomenon frequently seen in mines and caves. A man may enter these subterranean rooms, and feel no inconvenience in breathing; but the dog that follows him, falls apparently dead, and soon dies if not speedily removed to pure air. This arises from the fact that this gas is heavier than air, and sinks to the bottom of the room or cave.

3d. While it is true that carbonic acid possesses properties that render it unfit to be breathed, it is, notwithstanding, productive of very agreeable effects, when conveyed into the stomach. It forms the sparkling property of mineral waters, and fills the bubbles that rise when beer or cider is fermenting.

501. _Pure atmospheric air is best adapted to a healthy action of the system._ As the air cannot be maintained pure under all circ.u.mstances, the question may be asked, To what degree may the air be vitiated and still sustain life? and what is the smallest quant.i.ty of pure air a person needs each minute to maintain good health? Birnan says, that air which contains more than three and a half per cent. of carbonic acid is unfit for respiration, and, as air once respired contains eight and a half per cent. of carbonic acid, it clearly shows that it is not fitted to be breathed again.

502. No physiologist pretends that less than seven cubic feet of air are adequate for a man to breathe each minute, while Dr. Reid allows ten feet. The necessity of fifteen or twenty times the amount of air actually taken into the lungs, arises from the circ.u.mstance, that the expired air mixes with and vitiates the surrounding element that has not been inhaled.