320 THE GROWTH OF PLANTS AND ANIMALS 



by the sawmill, piledriver, or dynamo. In other words, 

 one form of energy, the sun's heat, has been converted 

 through the processes of growth, burning and the use 

 of machinery, into other forms, such as mechanical and 

 electrical energy. 



The animal body, an engine. The animal body in its 

 relation to the plant world is in some respects quite 

 in the position of the engine. It too is largely dependent 

 upon plants for the fuel, or food, which is necessary for 

 the development of its energy for growth and work. For 

 example, starch when eaten by animals is burned * in 

 the tissues for the production of heat and muscular 

 energy. 2 In this process there is just as much energy 

 developed in the form of muscular work and heat as 

 could be developed were the starch burned as fuel in 

 the most perfect steam engine. In fact, the animal body 

 is able to utilize in the form of muscular force, not 15 

 but 30 per cent of the total energy set free. The re- 

 maining 70 per cent takes the form of heat and serves 

 to maintain the temperature of the animal's body. 3 



As the muscular work done by animals increases in 

 severity, the amount of heat generated by the oxidation 

 increases in the same ratio. The result is that more 

 heat is generated than is necessary to maintain the 

 body's temperature, and the individual feels uncom- 



1 That is, oxidized, since all burning, whether rapid as in a fire 

 or slow as in decay, is due to the union of the oxygen of the air 

 with the carbon and hydrogen of the fuel ( food ) . 



2 Starch + oxygen = carb. diox. -f- water + heat 4- muse, energy 

 C 6 H 10 O 6 + 6 2 =6 CO 2 +6 H 3 + " + " 



In other words, 1 molecule of starch acted upon by 6 molecules 

 (12 atoms) of oxygen forms 6 molecules of carbon dioxide and 6 

 of water, and heat or heat and muscular energy are set free in 

 the process. 



8 In man, the normal temperature is 98.4 F. ; in the horse, 

 about 104 F.; in the ox and dog, 101 F.; in the sheep and pig, 

 103 F. ; and in the hen and pigeon, 107 F. 



