IS THE BODY A MACHINE ? 39 



what occurs as the foundation of respiration. The 

 blood coming to the lungs contains haemoglobin, 

 and since the oxygen pressure in the air is quite 

 high, this haemoglobin unites at once with a quan- 

 tity of oxygen while the blood is flowing through 

 the air-vessels. The blood is then carried off in 

 the circulation to the active tissues like the mus- 

 cles. These tissues are constantly using oxygen 

 to carry on their life processes, and consequently 

 at all times use up about all the oxygen within 

 their reach. The result is that in these tissues 

 the oxygen pressure is very low, and when the 

 oxygen-laden haemoglobin reaches them the as- 

 sociation of the haemoglobin with oxygen is at 

 once broken up and the oxygen set free in the 

 tissue. It passes at once to the lymph, from which 

 the active tissues seize it for the purpose of carry- 

 ing on the oxidizing processes of the body. This 

 whole matter of supplying the body with oxygen 

 is thus fundamentally a chemical one, controlled 

 by chemical laws. 



Removal of Waste. The next step in this life 

 process is one of difficulty. After the food and 

 oxygen have reached the tissues it is seized by 

 the living cell. The food material is now oxidized 

 by the oxygen, and its latent energy is liberated, 

 and appears in the form of motion or heat or 

 some other vital function. Herein is the really 

 mysterious part of the life process; but for the 

 present we will overlook the mystery of this action, 

 and consider the results from a purely material 

 standpoint. 



In a steam engine the fundamental process by 



which the latent energy of the fuel is liberated is 



that of oxidation. The oxygen of the air unites 



with the chemical elements of the fuel, and breaks 



4 



