124 HUMAN BIOLOGY 



combines, in the process of oxidation, with the carbon, 

 hydrogen, and other elements in the foods or protoplasm, 

 waste matters (carbon dioxid, water, etc.) are produced, and 

 for the healthy working of the body, these wastes must be 

 eliminated. We are now to see how the body is adapted 

 to secure an adequate supply of oxygen and to rid itself 

 of harmful waste matters. 



175. Respiration in plants, animals, and man. — It should 

 be clear from our study thus far that all living things require 

 oxygen, and that this oxygen brings about in plants, animals, 

 and man a process resembling oxidation, at least in the re- 

 leasing of heat and of other forms of energy, and in the pro- 

 duction of carbon dioxid and other waste matters. These 

 various processes doubtless take place in each living cell. 

 Hence, every cell must be supplied with oxygen and must 

 necessarily form carbon dioxid. The process by which plants 

 or animals take in oxygen and get rid of carbon dioxid is known 

 as breathing. And when we include also the oxidation that 

 takes place within the cells and the elimination of the wastes 

 from the cells, this whole series of processes is known as 

 respiration. 



Breathing involves two distinct processes; first, that of 

 taking into the lungs new supplies of fresh air, and secondly, 

 that of removing from the lungs the impure air that has been 

 used. To the first process is given the name inspiration 

 (Latin, in = into + spirare = to breathe) ; the second is called 

 expiration (Latin, ex = out + spirare = to breathe) . 



II. Adaptations for Securing Oxygen and for 

 Excreting Carbon Dioxid 



176. Course taken by the air. — In ordinary breathing, 

 air enters the body through the two nostrils (the left one is 



