ELEMENTS OF GENERAL SCIENCE 



285. Respiration. People often think of respiration as 

 merely involving the process of taking air into the lungs and 

 then expelling it That process is breathing and constitutes a 

 small and relatively superficial part of respiration. We breathe 

 ordinarily about eighteen times per minute, thus constantly 

 renewing the air within the lungs. 



As the blood flows through the thin walls of the tissues of 

 the lungs, some of the oxygen of the air combines with the red 

 coloring matter (haemoglobin) that is found in the red blood 

 corpuscles. When oxygen is combined with haemoglobin the 

 corpuscles are bright red. Therefore, when the blood has been 

 hi the lungs for a time and its red corpuscles have taken up a 

 load of oxygen, the blood is bright red and returns to the left 

 side of the heart with a distinctly different color from that 

 which it had when it was sent from the right ventricle. While 

 the blood is in the lungs it is also freed from the larger 

 part of its carbon dioxide, so that chemically the blood 

 leaving the lungs is quite different from what it was when 

 it entered them. It contains much less carbon dioxide and 

 much more oxygen. 



When the blood is pumped from the left ventricle through 

 the arteries to the tissues of the body, it carries digested food 

 material and a new supply of oxygen. Through the walls of 

 the capillaries the protoplasm of the tissues takes up digested 

 food and oxygen, and at the same time waste products from 

 broken-down protoplasm (carbon dioxide, for example) pass 

 into the blood. Oxygen is used by the protoplasm. When 

 protoplasm breaks down, energy is released, and this energy 

 keeps up the activity and life processes of all living things, 

 both animals and plants. It is this introduction of oxygen into 

 the tissues, and its use therein, that constitutes the most im- 

 portant part of respiration. Respiration includes the exchange 

 of the air in the lungs by breathing, the chemical change of the 

 air in the lungs, and the interchange of oxygen and carbon 

 dioxide in the tissues. 



