THE MASTER TISSUES 45 



form of carbon. Compounds containing these elements 

 are taken into the body through the digestive organs, 

 carried around by the fluid portion of the blood, and 

 stored up in the cells ready for union with oxygen by the 

 process of slow combustion, or slow oxidation, of which 

 the activity called animal life seems to consist. The oxy- 

 gen, on the other hand, enters the body through the lungs 

 and is carried to the tissues by the red corpuscles of the 

 blood. Thus is energy stored in the body, the oxygen 

 being ready to unite with the other elements, giving rise 

 to heat and motion. The rate and manner of this union 

 are regulated by one of the master' tissues, the nerves; 

 while the application of the energy so as to produce 

 motion is the function of the muscular tissue. 



74. The " burning" of food substances in the muscle is 

 essentially the same process as the burning of coal in the 

 furnace of the engine, but in the muscle the oxidation 

 takes place under peculiar conditions not at present thor- 

 oughly understood, at a temperature of less than 100 

 Fahrenheit, while for ordinary combustion a temperature 

 of several hundred degrees is required. 



75. The body resembles a locomotive in having warmth 

 and motion as a result of the union of fuel and oxygen ; 

 but it differs from the locomotive, since the intelligent 

 engineer is an organic part of it, and since the oxidation in 

 the body is in the presence of moisture, and so gradual 

 that it is not a true fire accompanied by light. Moreover, 

 the body can repair itself as it wears out, and the engine 

 cannot. The energy stored in the body is used more 

 economically and effectively than any steam engine can 

 use fuel. This we might well expect from the fact that 

 the engineer is a part of the engine. 



76. Muscular Tissue. How does the oxidation of food 

 produce motion ? We learn that the ameba and other 

 one-celled animals can change their shapes. Many of the 



