NATURAL THEOLOGY. 165 



T. What ivorks all this machinery ? 



A. Each room of the heart seems to work itself. 

 — The sides alternately contract and expand like a 

 bellows ; so that the cavities are continually filling 

 and discharging. The cause is unknown ; though 

 some think it is owing to a peculiar quality of the 

 blood. 



T. In fire engines there is a body of compressed 

 air, which is so contrived as to press the water out ; 

 because the stroke of the pump, which is only by 

 jerks, would not be capable of producing a steady mo- 

 tion. Is there any corresponding contrivance in the 

 heart, since here too the strokes are only by in- 

 tervals ? 



A. It is stated, that the arteries which receive 

 the rush of the blood from the heart are made elastic ; 

 this being the case, they enlarge when the blood is 

 thrown into them, and as soon as the discharge cea- 

 ses, contracting by their own spring, they press the 

 blood along in its course ; that is to say, they answer 

 the same purpose as the air vessel in the engine. 



B. One feels disposed to stop after this desrcip- 

 tion of the heart ; for it is impossible there can be 

 any thing so wonderful in any other part of the body, 

 as the mechanism you have described. 



T. We express our surprise at finding means em- 

 ployed in the living structure resembling our own 

 contrivances. But if they are such as would best 

 answer the purpose, what else could we expect to 

 find in the works of a Divine Architect ? But before 

 you have quite done with the circulating system, you 



