132 PHYSIOLOGY -AJSD HEALTH. 



tubes, and fills all the air-cells. On the other hand, when 

 the ribs fall, and the abdominal muscles press upon the 

 digestive organs, and force the diaphragm to rise, the lungs 

 are compressed, the air is expelled, and the air-cells closed. 



287. During life, there is a constant succession of these 

 actions. The air is at one moment drawn into the lungs, by 

 the contraction of the diaphragm and the lifting of the ribs, 

 and at the next moment it is expelled, by the falling of the 

 ribs and the contraction of the abdominal muscles. These 

 two operations constitute what is caHed respiration. Each 

 respiration supplies the lungs with a new quantity of air. 



288. This is the operation of respiration. All the parts 

 of its apparatus, the framework of bone, the muscles of the 

 ribs, and the diaphragm, all cooperate in the work, and are 

 necessary to effect its purpose, which is to bring the air 

 and the blood together, and to relieve the latter of its impu- 

 rities, and fit it for the support of the living body. 



CHAPTER IV. 



Waste Particles. Carbon. Air, Composition of. Oxygen 



Nitrogen. Affinity of Oxygen for Carbon. Carbonic Acid. 

 Carbon meets Oxygen in the Nutrient Vessels. Blood absorbs 

 Oxygen from the Air, and gives out Carbonic Acid. 



289. THE respiratory apparatus and its operation, which 

 carry out from the body the dead and waste particles, afford 

 striking evidences of Nature's skill, and beautiful illustra- 

 tions of her handiwork. The principal elements of this 

 waste matter, now mixed with the venous blood, are carbon 

 and hydrogen. These have a stronger affinity or attraction 

 for oxygen, one of the elements of the air, than they have 

 tor the fluid of the blood in which they move. 



290. Carbon is one of the most important elements of the 

 animal body. It enters into and forms a part of all flesh, 

 and of all vegetable matter. The brain, the muscle, the 



