io THE ENGINES OF THE HUMAN BODY 



have asked a friend to draw a simple plan of an internal- 

 combustion engine, built like the model used in my 

 lectures. It is important that we should note all the 



SPARKING PLUG 

 INLET VALVE EXHAUST VAL 



Fig. I. — A diagram to show the parts of which an internal-combustion engine is 

 made up. The piston is shown at the upper end of the cylinder at the be- 

 ginning of a stroke — the first downward or charge stroke. 



parts, because we shall have to search for corresponding 

 pieces and contrivances in the muscle-engines. 



First of all, there is the petrol tank (fig. i) containing 

 the fuel or food for the engine ; a " feed-pipe " runs 

 from the tank towards the upper end or head of the 



