OXIDATIONS IN THE BOM. 9& 



Oxidations in the body. In the preceding paragraphs 

 oxidation and burning have been used as equivalent 

 phrases : this is in accordance with the teachings of chem- 

 istry. To the chemist a substance is burned when it is 

 combined with oxygen, whether this combination take place 

 slowly or rapidly. If the combination occur rapidly the 

 burning or oxidizing mass becomes very hot and also gives 

 off light: such a rapid and vigorous oxidation is called a com- 

 bustion ; no combustions take pLice in our bodies. 



It has, however, been proved that whether the combi- 

 nation of oxygen with an oxidizable, or burnable, substance 

 takes place rapidly or slowly, at the end of the process ex- 

 actly the same amount of energy will have been set free in 

 each case. When the oxidation occurs in a few seconds the 

 oxidizing mass becomes very hot : when it occurs slowly, in 

 a few days or weeks, the mass will never be very hot, be- 

 cause the heat set free in the process is carried off nearly 

 as fast as it appears. 



Illustrations of oxidations at a low temperature. If a 

 piece of magnesium wire be ignited in the air it will 

 become white-hot, flame, and leave at the end of a few 



What does a chemist mean when he says a substance is burned ? 

 What is a combustion ? Do combustions occur in our bodies ? 



Does the quantity of energy liberated by the complete oxidation 

 of any substance vary with the rate of oxidation ? 



Why is a slowly oxidizing mass of matter not very hot ? 



Give an instance of the oxidation of the same substance at high 

 and low temperatures. 



the winter and take no food. They feed well in the warm weather, and are quite 

 fat at the close of autumn, when they seek some sheltered place to winter in. This 

 shelter and their warm, furry coats make the loss of heat very little; the animal, 

 except for its breathing and the beat of its heart, hardly ever moves during the 

 winter, and even those necessary movements are reduced to the least possible, the 

 breathing and heart-beat being much slower than during the summer. With return 

 of warm weather the creature wakes up again, but is then lean, having burnt up 

 its fat during its winter sleep. 



