io6 



Physiology. 



in the lungs from a dark bluish red to a bright scarlet. 

 This bright blood is usually called "arterial," and the dark 

 "venous"; but it must be remembered that the blood in 

 the pulmonary artery is dark, and in the pulmonary veins 

 bright. 



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Fig. 6 1 . Circulation in the Capillaries of the Lungs and in the Capillaries of the Body. 



The Changes in the Blood. What does the blood do 

 with the oxygen that it gets in the lungs, and where did it 

 get the carbon dioxid and other impurities that it brings to 

 the lungs ? Let us follow the blood and see. From the 

 pulmonary veins the blood goes to the left heart, and is 

 pumped to all the tissues except the lungs. Let us follow 

 a branch of the aorta that leads to a muscle. 



The Production of Heat and Motion in the Body. When 

 a muscle works it becomes warmer. The rise in tempera- 

 ture has been repeatedly proved by experiment. We know 

 that the blood is flowing more rapidly through the muscle 



