78 THE HUMAN BODY. 



but little in our food. Sulphur is one of these. Others 

 are abundant in the body, and are found in almost every 

 article of food. Carbon is one of these. If any of these 

 elements is entirely wanting in our food, we suffer, and 

 would starve to death for lack of some of them. If we 

 should try to live on food which contained no phosphorus, 

 for example, we should become diseased, and die. Almost 

 every thing that we eat contains phosphorus. 



5, Other elements than the fifteen given above, are not 

 required in our food. Silver, for example, does not form 

 part of the body, or of our food , but nitrate of silver is 

 sometimes used as a medicine. 



6, All of these fifteen elements are found in the air, the 

 earth, and the water. But animals can not feed on earth 

 and air and water. Plants can, and that is one of the 

 great distinctions between plants and animals Four- 

 fifths of the air is nitrogen. But men, and other animals, 

 would die for want of nitrogen, even while they were 

 drawing it into their lungs with every breath, if they 

 could not get food containing it. 



7, It is the ivork of plants to take the elements, and make 

 them into food for animals. The plant feeds on earth, 

 air, and water. This earth, air, and water become a part 

 of itself. The animal feeds on the plant, or on other 

 animals. 



8, Probably every plant is food for some animal. But 

 there are very many which are not food for man. Some 

 are poisonous. A large number contain the necessary 

 elements, but can not be digested by the human organs of 

 digestion. A fertile prairie which would fatten a herd of 

 buffaloes would starve a man; because the grasses, though 

 not poisonous or distasteful, contain too much indigest- 

 ible matter for his stomach. 



