NUTRIENTS 
13 
hydrogen and oxygen to form sugar, starch, fat, and wood. 
Charcoal is a form of carbon. It is made by burning wood 
with a small amount of oxygen. Coal is almost wholly carbon, 
while the diamond is carbon in the form of a crystal. 
Nitrogen. — This element is an inactive gas and it does not 
readily combine with other elements. It dilutes the oxygen 
of the air, making it less active. Nitrogen comprises four 
fifths of the volume of the air. It is an important plant and 
animal food. Nitrates are compounds of nitrogen, oxygen, 
and some other elements. Potassium nitrate is a com¬ 
pound of nitrogen, oxygen, and potassium. Sodium nitrate 
is a compound of nitrogen, oxygen, and sodium. Such 
nitrates are the forms in which nitrogen can be used as plant 
food. Plants are unable to use the nitrogen of the air as a 
food directly. Proteins are animal and plant products that 
contain nitrogen. Proteins are necessary food for animals, 
and animals are dependent on plants to furnish these sub¬ 
stances. See pages 278-280. 
There are other elements that are needed in small amounts 
by animals, such as calcium, phosphorus, sulphur, potassium, 
and iron. The human body is made up of: 
oxygen 
72 
parts 
phosphorus 
1.15 
parts 
carbon 
13.5 
u 
sulphur 
.147 
ii 
hydrogen 
9.1 
n 
potassium 
.026 
ii 
nitrogen 
2.5 
u 
iron 
.01 
ii 
calcium 
1.3 
ii 
Nutrients. — The elements above, while forming the body 
structure, are not taken directly as food. The foods we 
commonly use have these elements in combination with other 
materials. The foods that contain the proper elements are 
spoken of as nutrients. These nutrients are starches, 
sugars, proteins, edible fats, and mineral matter. 
Starch is a nutrient that occurs in many of our foods. 
Potatoes, corn, wheat, rye, rice, and most of the vegetable 
