102 LABORATORY MANUAL 



their distribution. Crush a portion of a nodule on a 

 glass slide and mount a portion of the material in a 

 drop of water. Cover with a cover glass. With the 

 aid of the instructor, find the mass of moving bacteria 

 under the high power microscope. Sketch to show the 

 form of some of the bacteria. These bacteria are very 

 helpful to the plants of the pulse family, enabling 

 them to obtain and utilize the nitrogen from the air as 

 food. 



CHAPTER XVI 



CLASSIFICATION OF FOODS 



Substances which are taken into the body as nourish- 

 ment are known as foods. 



Foods contain many elements, chief of which are 

 carbon, hydrogen, oxygen, nitrogen, sulphur, phos- 

 phorus, and iron. 



These elements do not occur in living matter as 

 elements, but in various combinations or compounds. 

 These compounds in foods are known as foodstuffs. 

 There are five such foodstuffs. 



Proteins, or nitrogenous compounds. 



Carbohydrates, or starches and sugars. 



Hydrocarbons, or fats and oils. 



Mineral salts. 



Water. 



