Fig. 57—Under surface of a geranium leaf showing breathing pores, highly magnified (O.H.).
Summary.—Oxygen, by uniting with materials at the cells, keeps up a condition of chemical activity (oxidation) in the body. This supplies heat and the other forms of bodily energy. Entering as a free element, oxygen leaves the body as a part of the waste compounds which it helps to form. The free oxygen is transported from the lungs to the cells by means of the hemoglobin of the red corpuscles, while the combined oxygen in carbon dioxide and other compounds from the cells is carried mainly by the plasma. The limited supply of free oxygen in the body at any time makes necessary its continuous introduction into the body.
[pg 113]Exercises.—1. Describe the properties of oxygen. How does it unite with other elements? How does it support combustion?
2. State the purpose of oxygen in the body. What properties enable it to fulfill this purpose?
3. What is the proof that oxygen does not remain permanently in the body? How does the oxygen entering the body differ from the same oxygen as it leaves the body?
4. What is the necessity for the continuous introduction of oxygen into the body, while food is introduced only at intervals?
5. How are the red corpuscles able to take up and give off oxygen? How is the plasma able to take up and give off carbon dioxide?
6. If thirty cubic inches of air pass from the lungs at each expiration and 4.5 per cent of this is carbon dioxide, calculate the number of cubic feet of the gas expelled in twenty-four hours, estimating the number of respirations at eighteen per minute.
7. What is the weight of this volume of carbon dioxide, if one cubic foot weigh 1.79 ounces?
8. What portion of this weight is oxygen and what carbon, the ratio by weight of carbon to oxygen in carbon dioxide being twelve to thirty-two?