138 
SECOND BOOK. 
engine fire with fuel there is soon no steam from 
the boiler, and then the work ceases. So, too, your 
body would soon cease to live and have power if it 
were not fed. 
9. “ Again, the engine needs repairing some- 
times. The parts and organs of your body are also 
constantly wearing out, and this wasting or wearing 
has to be made good or repaired every day by the 
food you take.” 
“ The engine must have water too, and so must 
we,” said May. “ I have read about a traveller who 
died in the desert for want of water.” 
10. “ Yes,” said Miss Brooks. “ Besides, there 
must be a good draught of air to the fire. And, for 
the slow burning of the food in your body, you are 
fed by the oxygen of the air you breathe into your 
lungs. 
“ Of course,” she continued, “ what we eat must 
contain whatever is in the flesh, bone, blood, and 
nerve of our bodies. We must give back the 
same kind of substances that are wasted or lost. 
n. “ Now, our bodies contain much water, and 
plenty of this is therefore needed. We not only 
take it as a drink, but it is present in all the foods 
we eat. Then, our bones are partly formed of 
lime, and other minerals are also found in the 
body. So we must take in a supply of all these 
materials. 
12. “ At present I will say no more about the 
