FOODS 67 



energy than are the carbohydrates. They also furnish fuel 

 for the running of the body mechanism. 



V. The proteids form a large part of all living organisms 

 and are absolutely necessary to animal life. They are very 

 stable compounds and are found in both animal and vegetable 

 foods. They contain carbon, hydrogen, oxygen and nitro- 

 gen, together with, usually, a small quantity of sulphur and 

 phosphorus. They occur in the form of casein in milk and 

 cheese, myosin and syntonin in muscle, vitellin in the yolk of 

 eggs, glutein in flour, legumin in peas, beans and lentils, and 

 in some other forms. Proteids may be used by the body to 

 produce heat and energy, but being more stable in composi- 

 tion than carbohydrates and fats, they are more often used 

 to build up tissue. In fact the proteids are absolutely essen- 

 tial to life while this is not true of carbohydrates and fats, 

 since the proteids must be used to build up new cells to take 

 the place of those being constantly worn out and eliminated. 



The animal foods which are richest in proteids are lean 

 meat, milk, eggs, cheese and all kinds of fish, while the vege- 

 table are wheat, beans, peas and oatmeal. It has been found 

 that the animal proteid foods are split up and digeste'd much 

 more easily than are the vegetable. Hence the great ma- 

 jority of the people rely upon the animal foods for their sup- 

 ply of proteid material which is necessary to life. 



The composition of a few of the more important articles 

 used as food is shown by the following tables.* 



Milk : Woman, Cow, 



Per cent. Per cent. 



Protein (chiefly caseinogen) 1.7 3.5 



Butter (fat) '..... 3.4 3.7 



Lactose 6.2 4.9 



Salts 0.2 0.7 



Eggs : 



Total amount of solid 13.3 per cent 



These tables are taken from Halliburton's Handbook of Physi- 

 ology. 



