AND AGRICULTURE. 79 



sume daily some substance which will yield that 

 amount of carbon to his system, or he must soon 

 become the subject of impaired health. Fifteen 

 ounces of starch contain about seven ounces and 

 three-quarters of carbon ; so that his food must 

 be equal, in the carbon it contains, to a little 

 more than fifteen ounces of starch. 



The carbonic acid gas thrown off from the 

 lungs is diffused in the atmosphere, to be again 

 taken up by plants, again by them to be re- 

 transformed into starch, or substances similar in 

 composition thereto. Thus you see how beauti- 

 fully, in the economy of nature, the processes 

 of reproduction are perpetuated. The same car- 

 bon is again and again transformed by the 

 plant into starch, and by the animal into car- 

 bonic acid. The animal transforms the carbon 

 into carbonic acid gas, by a process of combustion, 

 necessary to keep up its warmth ; and, in the 

 process of vital combustion, a portion of the 

 carbon combines with a portion of the oxygen of 



Questions. How much starch, or its equivalent, must a 

 man consume daily ? What becomes of the carbonic acid 

 gas thrown from the lungs ? Is the same carbon again and 

 again reproduced and consumed ? How is the carbonic acid 

 gas produced by the animal from the carbon taken in his 

 food? 



