CHAPTER VIII 



RESPIRATION 



The Objects of Respiration The Lungs The Air-passages The 

 Movements of Respiration Expiration and Inspiration The Fre- 

 quency of Respiration Capacity of the Lungs The Air we Breathe 

 Changes in the Air from Respiration Changes in the Blood 

 Interchange of Gases in the Lungs Comparison between Arterial 

 and Venous Blood Respiratory Labor Impurities of the Air 

 Dust Carbonic Acid Effects of Impure Air Nature" 1 s Provision 

 for Purifying the Air Ventilation Animal Heat Spontaneous 

 Combustion 



1. The Object of Respiration. In one set of capillaries, or 

 hair-like vessels, the blood is impoverished in order to support 

 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 cir- 

 culation; the 'latter to the lesser or pulmonary, 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 hurtful to 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 injuri- 

 ous. 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 respi- 

 ration. There are two of them, one on each side of the chest, 

 which cavity they, with the heart, almost wholly fill. The 

 lung-substance is soft, elastic, and sponge-like. Under pres- 

 sure of the finger, it crepitates, or crackles, and floats when 



1. Difference between the two sets of capillaries ? Change effected by respiration or 

 breathing ? 



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

 ties ? The pleura ? 



M 177 



