86 SCIENTIFIC AGRICULTURE. 



plicated in its structure than that of a plant. In the 

 higher animals it consists of a bony skeleton, covered 

 with flesh, through which runs a network of nerves 

 and blood-vessels. Within a portion of this skeleton 

 are placed the lungs and digestive organs. Solid 

 and liquid food passes through the mouth into the 

 organs of digestion, where the portion suitable for 

 conversion into flesh is made soluble by means of 

 proper secretions. This nutritive portion is absorbed 

 by suitable organs, carried into the blood, and then 

 distributed to all parts of the body, where it be- 

 comes flesh and bone by a mysterious process which 

 has never been explained. The operation is so deli- 

 cate and complicated, and so many organs or parts 

 are necessary to have it carried on successfully, that 

 it is no wonder animals cannot thrive when badly 

 treated. 



194. It is well known that oxygen of the air is 

 as necessary for animal life as for the burning of 

 wood and coal in our fireplaces, and that air com- 

 ing from the lungs in breathing is charged with car- 

 bon dioxide. This can easily be shown by breathing 

 through clear lime-water by means of a glass or oth- 

 er tube. The water becomes milky, a result caused 

 by the carbon dioxide from the lungs combining 

 with the lime in solution to form insoluble calcium 

 carbonate. Just as the chemical action, or burning 

 of fuel in a fireplace or under a steam-boiler, pro- 

 duces heat and force, or energy, enough to move 

 machinery, so the chemical action within the body 



