FOOD 113 



need an engineer or fireman. It is a self -con trolling 

 machine and is also able to obtain the fuel necessary 

 to keep it in an active state. 



78. Cells. The whole human body may be thought 

 of as a living organism which is made up of parts called 

 organs, such as the heart, the lungs, the hands, etc. 

 Each organ is made up of several tissues. For example, 

 the heart is composed of muscular 

 tissue, nervous tissue, connective 

 tissue, and a few others. Each 

 tissue is made up of smaller parts 

 called cells. A cell is the smallest 

 division of a living body which can 

 do the things necessary to sustain its 



life and that of the body of which the FLAT C THE 

 cell is a part. The cells can take 

 in food, can breathe, can throw off waste matter such as 

 carbon dioxide and nitrogen compounds, and can grow 

 and make other cells. These are called the functions 

 of life. 



In order that cells may carry on such activities, it is 

 necessary for them to have a continuous supply of food, 

 and the more active they are as when a person is at 

 work the more food they need. There is no time when 

 all the cells of the body are at rest, and on this account 

 it is necessary to take food even when we are not at con- 

 tinuous or regular work. The cells in the human body 

 keep up a continuous work of reconstruction and growth 

 in order that the whole body may be in the best possible 

 condition of health. When not enough exercise is taken 

 to cause the waste matter of the cells to be carried away 

 as fast as it is produced, and to cause a fresh supply of 

 food to be carried to the cells, then the cells are not able 



