PHYSIOLOGY OF VEGETABLES 109 



Windpipe, which every where accompany them, being 

 separated from them only by very fine membranes. 



In these extreme vessels of the lungs the blood under- 

 goes an important change* It gives off a portion of 

 its carbon which combines with a portion of the oxy- 

 gen or vital air inspired ; at the same time its capaci- 

 ty for caloric or heat is increased, and it drinks up, as 

 it were, the heat of the oxygen, which otherwise would 

 have been developed. By these changes, the blood 

 from a purple, acquires a bright verm ill ion colour. 

 The blood then passes into the left cavity of the head, 

 which contracts and throws it through the arteries in- 

 to the extreme vessels of the body, still retaining its 

 vermillion colour. 



In the extreme vessels of the body 9 the blood performs 

 the important offices for which it was designed in the 

 animal economy. In these, in some unknown manner, 

 its capacity for the matter of heat, is diminished, and 

 the heat which was taken up in the lungs is thus devel- 

 oped, where it is required, in every part of the body. 

 In these vessels also, the body is nourished and its de- 

 cays built up. 



After the blood has passed the extreme vessels, it is 

 found to have lost its fine vermillion, and acquired a 

 dark purple, which it retains as it passes through the 

 veins to the heart, and thence to the lungs, to be re- 

 newed arid recirculated. 



Another system of vessels called t\\eLacteals 9 take up 

 from the viscera the essential nourishment of our food, 

 and convey it by their common trunk, to the circulation 

 emptying it, in form of milk into one of the veins. 

 Thus the great business of the circulation is done in 

 in the extreme vessels of the lungs and in those of the 

 body ; the larger trunks serve as mere channels of con- 

 veyance, while the heart acts as an engine to give mo- 

 tion. In the extreme vessel:-; of the lungs the blood is 

 prepared to nourish and support the body, and in th we 

 of the body it performs this office. 

 10 



