hi /;Gr f r/'y/.LV AGRICULTURE, 



oxygen gas being taken into the living body where it is 

 used to unite with other substances for the production of 

 heat and vital energy. Life is an active condition and 

 without the production of energy, activity and life are 

 impossible. In the body, energy is only produced by the 

 < < mi bustion of the food materials. With few exception s, the 

 combustion taking place in the animal or plant body consists 

 in the oxidation of the organic substances of the food. 



It is of the greatest importance that the agriculturist 

 should understand the ordinary phenomenon of burning 

 or combustion. Combustion is the union of oxygen with 

 some other substance. When oxygen unites with iron, 

 "rust" is formed and heat is given out; when it unites 



with the carbon in wood, carbon dioxide and heat result 







from the combination. Combustion or oxidation may 

 be rapid or slow. Rapid combustion produces much heat 

 in a short time which results in a high temperature 

 with perhaps the production of light, whereas slow com- 

 bustion may be invisible. If a piece of sugar or starch 

 is burnt in the air or oxygen a high temperature is pro- 

 duced. If an animal or plant consumes an equal quantity 

 of sugar or starch, the same amount of heat is produced 

 in its oxidation in the living body, but the combustion is 

 slower and takes place at a lower temperature. In the 

 animal or plant, sugar and starch are burnt at a little over 

 the body temperature whereas in the air a hot flame must 

 be applied before combustion will begin. This power to 

 combust or oxidize bodies at a low temperature is one of 

 the attributes of life. From combustion, heat is produced; 

 and this heat may be used to drive engines and do other 



