LESS. VI FOOD AND FOOD-STUFFS 225 



which it is then distributed over the body. We may 

 therefore most suitably begin by learning something of 

 the nature and composition of that " new material " which 

 we introduce into the body as food. 



2. Food and Food-stuffs. — Every one is famUiar with 

 the meaning of the term food, as exemplified by bread, 

 meat, potatoes, milk, etc. None of these substances, 

 however, is made up of one kind of material ; but when 

 analysed it is found that they all consist of varj-ing 

 amounts of a few substances, and to these the name of 

 food-stuflfe is given. 



Food-stuffs are classified under four heads, (1) Pro- 

 teins, (2) Fats, (3) Carbohydrates, (4) Salts 

 (mineral matter) and Water. They may further be 

 divided into two distinct groups : — the nitrogenous and 

 the non-nitrogenous. The proteins alone contain 

 nitrogen and thus form one group by themselves ; the 

 other food-stuffs are all non-nitrogenous. Further, the 

 first three classes, as being compounds of carbon, are 

 known as organic compounds, while the salts and water 

 are inorganic. They may therefore be tabulated as 

 follows : — 



Organic Inorganic 



(Nitrogenous) (Non-nitrogenous) (Non-nitrogenous) 



Proteins Fats Salts 



i I' 



Carbohydrates Water 



A. Nitrogenous Food-Stuffs. 



Proteins. — These are composed of the four elements 

 carbon, oxygen, hydrogen and nitrogen united with 

 small amounts of sulphur (see p. 108). Under this 

 head come the albumin of the white of egg, and 

 blood-serum ; the casein of milk and cheese ; the 



