226 ELEMENTARY PHYSIOLOGY less, 



gluten of flour and other cereals ; the myosin of lean 

 meat (muscle) ; the globulins of blood and of the yolk 

 of an egg and the jQbrin of blood. 



Gelatin, the basis of connective tissue fibres, contains, 

 like protein, carbon, hydrogen, nitrogen, and oxygen 

 in the proportions in which they occur in protein, and 

 may be regarded as an outlying member of this group. 

 But gelatin contains no sulphur and cannot entirely 

 replace protein in food. 



B. Non-nitrogenous Food-Stuffs. 



(i) Fats. — These are composed of carbon, oxygen, and 

 hydrogen only, and contain less oxygen than would form 

 water if united to the hydrogen they contain. Butter 

 and all animal and vegetable oils come under this head. 



(ii) Carbohydrates. — These are substances which also 

 consist of carbon, oxygen, and hydrogen only, but in 

 them the oxj^gen is present in an amount which would 

 just suffice to form water if it were united to their hydro- 

 gen. This group includes starch, as in flour or potatoes ; 

 ordinary cane-sugar or beet-sugar, and other sugars 

 such as dextrose and mUk-sugar ; also cellulose 

 from all vegetable tissues. 



(iii) Salts and Virater. — Water is present in all foods, 

 and salts in most of them such as meat, eggs, milk, and 

 cheese. The salts are chiefly the phosphates, chlorides, and 

 carbonates of sodium, potassium and calcium, and some 

 salts of iron. 



All food is made up of these food-stufFs, but the 

 amount of each present in different foods varies greatly. 

 Thus meat is chiefly protein, but ordinarily contains a 

 good deal of fat ; bread contains a great deal of carbo- 

 hydrates, but also some protein and a little fat. Only the 

 fats and oils may be regarded as composed of nearly pure 

 material. The composition of the chief foods is important 

 and has been carefully determined ; but to this we shall 

 return when we come to study their respecti ''^influence on 

 the body as a whole. 



