THE BODY DIFFERS FROM OTHER MACHINES 353 



which we shall see later. The human machine, however, 

 does more than do work. Unlike the auto or the loco- 

 motive, with proper 

 care, it can grow 

 larger and stronger 

 or with abuse, it can 

 waste away, become 

 weaker, or even die. 



liquid oXxsfcas- 



eteom pushes 

 a piston* 



lY7e-wh*l* 



Ccxrfoon dioxicte 

 anct water vapor^ 



released: 



Explain this cartoon in your workbook. 



The food it consumes SEE 1 2^*- f ^V ******** 

 is not all fuel, for the 

 human machine grows 

 and is to some ex- 

 tent regulated by 

 foods which, as we 

 have seen in a previ- 

 ous unit, are not used 

 as fuels. In this re- 

 spect the human machine is very different from the 

 man-made auto or locomotive. 



In order to grow, that is, gain in weight and size, the 



body uses the various 

 chemical elements in the 

 foods, building them in- 

 to complex combinations 

 which make up the living 

 matter of the body. This 

 living matter is built up 

 of millions of tiny units 

 called cells. You have 

 all noticed that a brick 

 building when seen from 

 a distance does not show 



Just as this house is made of bricks, so the the individual bricks, 



plants and our bodies are made of cells, the g() ^ the human body 



units of structure in living things. Can you . - 



see the cells in your body ? WC Cannot SCC these tiny 

 H. & w- sci. 1 24 



