RESPIRA TION. 1 1 3 



5. Inspiration acts in opposition to resistances, whose elastic re- 

 action performs ordinary expiration without active effort 



6. There are four heart beats for each respiration. 



7. The lungs are never emptied. 



8. Respiratory capacity may be increased by exercise and practice. 



9. Respiration is controlled by the nervous system ; the respiratory 

 center is in the spinal bulb. 



10. Internal respiration is an oxidation in the tissues, illustrated by 

 the rusting of moist iron. 



u. In passing through the lungs air loses oxygen, and gains water, 

 carbon dioxid, and other wastes. 



12. Oxygen is carried chiefly by the colored corpuscles of the blood ; 

 it unites with hemoglobin in the corpuscles, forming oxyhemoglobin, 

 and gives the blood its bright scarlet color. 



13. The energy of heat and motion in the body results from the 

 oxidations in the tissues. 



14. Air once breathed is unwholesome. The air of living and sleep- 

 ing rooms needs constant renewal. 



Questions. i . Is it a good thing to see how long one can hold his 

 breath ? 



2. Should the head be covered by bedclothes? 



3. What are the "lights " in an animal? 



4. How is respiration affected by a stooping posture? 



5. In what part of the lungs is the best air? Where the worst? 



6. Can you explain how respiration affects circulation ? 



7. Is it easy to determine by the color of blood flowing from a 

 wound whether it is arterial or venous? Why? 



8. Of what advantage is it that the cartilages of the windpipe are 

 C-shaped and not complete rings? 



9. How is it that in respiration 5 per cent of the oxygen disappears 

 while only 4 per cent of carbon dioxid appears in its place in the 

 expired breath ? (See p. 102.) 



