82 THE VITAL FUNCTIONS 



The same chemical process (oxidation) takes place 

 when we burn sugar in the air, the same products, 

 carbon dioxide and > water, and kinetic energy in the 

 form of heat, resulting. When we burn coal or petrol 

 in an engine a similar process takes place. Here the 

 kinetic energy is partly used to drive a machine, for 

 instance a steam locomotive or a motor car, and this 

 mass motion is comparable with the mass motion of 

 protoplasm. In both cases some of the energy appears 

 as heat, raising the temperature of the cell or of the 

 engine, as the case may be. 



The living protoplasm of all plants requires free 

 oxygen for respiration just like that of animals, though 

 plants do not use it so quickly as active animals do. 

 In green plants in light respiration is masked, because, 

 as we shall see in a later chapter, the opposite process — 

 the formation of sugar from carbon dioxide and water, 

 with production of free oxygen — is carried out at a 

 greater rate than respiration. In plants (and in parts 

 of plants) that are not green and are growing quickly, 

 i.e. expending much energy, for example in germinating 

 seeds and opening flower buds, a great quantity of 

 oxygen is used, and has to be taken from the air, and 

 a great deal of carbon dioxide and heat are produced. 



" Breathing " in the higher animals, also called 

 " respiration," ^ consists of the rhythmically alternating 

 processes of " inspiration " and " expiration." The 

 former is the taking of air into the lungs so that oxygen 

 may be absorbed through the walls of the lung tissue 

 by the haemoglobin of the red blood corpuscles, and 

 carried by them in the blood stream to all the tissues 

 of all the organs of the body, where respiration in the 



« This of course is the original meaning of the term (from Latin 

 spiro, breathe). 



