44 THE PLANT. 



parts ; and food, in order to satisfy the demands of 

 animal life, must contain the mineral matter re- 

 quired for the purposes of that life. Take bones for 

 instance. If phosphate of lime is not always sup- 

 plied in sufficient quantities in the food, animals are 

 prevented from forming healthy bones. This is par- 

 ticularly to be noticed in teeth. Where food is 

 deficient of phosphate of lime, we see poor teeth as 

 a result. Some physicians have supposed that one 

 of the causes of consumption is the deficiency of 

 phosphate of lime in food. 



The first class of vegetable constituents (starch, 

 sugar, gum, etc.) perform an important office in the 

 animal economy aside from their use in making fat. 

 They constitute the/WZ which supplies the animal's 

 fire, and gives him his heat. The lungs are the 

 delicate stoves, which supply the whole body with 

 heat. But let us explain this matter more fully. If 

 wood, starch, gum, or sugar, be burned in a stove, 

 they produce heat. These substances consist, as 

 will be recollected, of carbon, hydrogen, and oxygen, 

 and when they are destroyed in any way, (provided 

 they be exposed to the atmosphere,) the hydrogen 

 and oxygen, unite and form water, and the carbon 

 unites with the oxygen of the air and forms carbonic 

 acid, as was explained in a preceding chapter. This 

 process is always accompanied by the production of 

 heat, and the intensity of this heat depends on the 

 time occupied in its production. In slow decay, the 

 chemical changes take place so slowly that the heat, 

 being conducted away as soon as formed, is not per- 



