NATURAL THEOLOGY. 163 



to go over the same process of being first received 

 from the body and propelled into the lungs, — and 

 then received from the lungs and propelled into the 

 body, by two separate engines, as long as life shall 

 last. 



Fig. 30. 



A Fire Engine of the simplest construction. 



a, the receiving hose emptying the water into b, the receiving 

 room, — whence it passes into d, the forcing room, through c, 

 a little orifice with a valve or clapper over it, opening into 

 the forcing room, the valve shutting down and closing the 

 orifice, when the forcing instrument g, d, descends. The 

 water is then forced out into/, the delivering hose, through c, 

 another little orifice with a valve over it, which ojpens into 

 the hose, and prevents the return of the water into the forcing 

 room. The dotted line represents the course of the water. 



