250 PRINCIPLES OF GARDENING. [CH. VIII. 



cisely similar ; its colour and flavour are altered, and 

 its specific gravity increased. 



From its stomacli the animal's food passes into the 

 intestines, is there subjected to the action of the 

 bile, and the chyle or nutritive portion separated 

 from that which is excrementitious. In its pas- 

 sage through the intestines, the chyle is absorbed by 

 the lacteal vessels, and conveyed into the blood ; and 

 these mingled liquids are propelled by the heart into 

 the lungs, to be there exposed to the action of the 

 air. The vital liquid now changes its pui'ple hue to 

 a florid red, loses a portion of its carbon and watery 

 particles, the former combining with the oxygen of 

 the atmospheric air in the lungs, and being breathed 

 forth in the form of carbonic acid gas. As plants 

 take in as food no gross, imneeded ingredients, it is 

 obvious that no process like the biliaiy operation is 

 required in their course of digestion. But in them 

 the food or sap, proceeding at once along the branches, 

 is poured into the leaves, which are the very lungs of 

 the vegetable world. Here, as is the blood, its 

 colour is changed, and oxygen emitted from it dur- 

 ing the light hours of the twenty-four ; but carbonic 

 acid is breathed forth during the night, and, at all 

 periods, a considerable amount of wateiy vapour is 

 emitted. 



From the lungs, by the agency of the heart, the 

 blood is propelled through the arteries over the whole 



