_Illustration._ When spirituous liquors are taken into the stomach, they are absorbed by the veins and mixed with the dark-colored blood, in which they are carried to the lungs to be expelled from the body. This will explain the fact, which is familiar to most persons, that the odor of different substances is perceptible in the breath, or expired air, long after the mouth is free from these substances. -=-=-=-=-=-=-=-=-=-=-=-= How the watery vapor? 494. Are there other excretions from the lungs? Give the illustration. -=-=-=-=-=-=-=-=-=-=-=-= _Note._ Let the anatomy and physiology of the respiratory organs be reviewed from figs. 96, 97, and 99, or from anatomical outline plates Nos. 5 and 7. CHAPTER XXV. 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 circumstances. 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 quantity 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 quantity 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? -=-=-=-=-=-=-=-=-=-=-=-=