Rural School Leaflet 873 



worn-out tissues in the adult. Carbohydrates furnish energy that is 

 usually soon expended in the form of motion. Fats furnish energy mostly 

 in the form of heat. These are not absolute uses, but are the chief uses. 

 Mineral matter builds bones and performs other functions. Water acts 

 as a cleansing and transporting agent. Water also acts as a diluting 

 agent which prevents too great concentration of nutrient. 



When more carbohydrate is eaten than is immediately used by the work 

 of the body, the extra amount is stored as fat. This fat is used up in a 

 time of need. Too much fat reduces the power of the muscles. Too 

 much carbohydrate in proportion to the protein fed to a cow tends to 

 produce fat instead of milk. 



The most important constituent of Hving matter is protein. One great 

 difference between proteins and carbohydrates is that proteins contain an 

 element called nitrogen and carbohydrates do not. A diet or ration con- 

 taining no protein could not maintain life, as the tissues would gradually 

 waste away and death from starvation would be the result. Fats and 

 carbohydrates alone would not be sufficient to keep an animal alive. 

 Thus we find that whatever else is considered in the balancing of a diet 

 or ration, the question of including protein of some kind in proper 

 amounts must receive attention. 



Most of the food received into the body is in solid form. Before this 

 food can be taken up by the blood and distributed to the various parts 

 of the body, it must be dissolved and so changed that the cells of the body 

 can use it. The process of so changing the food is called digestion. The 

 mouth, stomach, and intestines are the places where these changes are 

 made. Proper cooking of food assists in this work. 



(i) Compare the digestive process of the cow with your own. (See 

 page 75.) 



(2) In what parts of the digestive system are the various nutrients 

 acted upon? 



After the food is digested it is taken into the blood (some directly and 

 some through the lymphatic system) and carried to all parts of the body. 

 The various cells feed on this prepared food. They grow and develop. 

 The blood also brings oxygen to these cells. The oxygen acts on the cells 

 to free their energy in the form of heat or motion, much as the oxygen 

 of the air acts on the coal or wood in the stove to free the energy of the 

 wood cells in the form of heat. The blood then carries away the waste 

 material. This waste material corresponds in a way to the gases that 

 go up the chimney and the ashes that are removed from the stove. 



This process of building up and tearing down is constantly going on in 

 all living things. Life is directly dependent on the keeping up of this 

 work. 



35 



