RESPIRATION. 123 



CHAPTER VIII. 

 RESPIRATION. 



The Objects of Respiration The Lungs The Air-Passages The Move- 

 ments of Respiration Expiration, and Inspiration The Frequency 

 of Respiration Capacity of the Lungs The Air we breathe 

 Changes in the Air from Respiration Changes in the Blood In- 

 terchange of Oases in the Lungs Comparison between Arterial and 

 Venous Blood Respiratory Labor Impurities of the Air Dust 

 Carbonic Acid Effects of Impure Air Nature's Provision for 

 Purifying tJie Air Ventilation Animal Heat Spontaneous Com- 

 bustion. 



1. The Object of Respiration. In one set of capil- 

 laries, or hair-like vessels, the blood is impoverished for the 

 support of the different members and organs of the body. 

 In another capillary system the blood is refreshed and again 

 made fit to sustain life. The former belongs to the greater 

 or systemic circulation ; the latter to the lesser or pulmo- 

 nary, so called from pulmo, the lungs, in which organs it 

 is situated. The blood, as sent from the right side of the 

 heart to the lungs, is venous, dark, impure, and of a nature 

 unfit to circulate again through the tissues. But, when 

 the blood returns from the lungs to the left side of the 

 heart, it has become arterial, bright, pure, and no longer 

 hurtful to the tissues. This marvellous purifying change 

 is effected by means of the very familiar act of respiration, 

 or breathing. 



2. The Lungs. The lungs are the special organs of 

 respiration. There are two of them, one on each side of 

 the chest, which cavity they, with the heart, almost wholly 

 occupy. The lung-substance is soft, elastic, and sponge- 

 like. Under pressure of the finger, it crepitates, or crackles, 

 and floats when thrown into water ; these properties being 



1 . Difference between the two sets of capillaries ? Change effected by respira- 

 tion or breathing? 



2. What are the lungs? How many lungs are there? Lung-substance? Its 

 properties ? The pleura ? 



