96 



excrementitious matter. In their passage through 

 the intestines the chyle is absorbed by the lacteal 

 vessels, and is conveyed into the blood ; by the heart, 

 the mingled fluids are propelled into the lungs, to be 

 there exposed to the action of the air. The vital 

 fluid there changes its purple hue for a florid red, 

 loses a portion of its watery particles and carbon ; 

 the latter combining with the oxygen of the atmos- 

 pheric air in the lungs, and being breathed forth in 

 the form of carbonic acid gas. 



As plants in their food take in no gross, unneces- 

 sary ingredients, it is obvious that no process like the 

 biliary operation is required. The lymph or sap, pro- 

 ceeding at once along the branches, is poured into the 

 leaves, the very lungs of plants. There, as in the 

 blood, its colour is changed, oxygen is emitted from 

 it during the light hours of the day ; but carbonic 

 acid gas is thrown off during the night, and at all 

 periods a considerable quantity of water. 



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

 blood is propelled through the arteries over the whole 

 animal system, supplying nourishment and warmth 

 to all the parts, and where, by these abstractions, it is 

 again converted into purple or venous blood, it is re- 

 turned by the veins to undergo the changes that were 

 described as being effected by the lungs. 



The sap, after exposure to the action of the air in 

 the leaves, is returned by another set of vessels situate 



