128 CHANGES IN BLOOD IN THE LUNGS. 



While the amount of nitrogen remains about the same, 

 some oxygen has disappeared, and its place is taken by carbon 

 dioxid, while the amount of carbon dioxid has increased a hun- 

 dred-fold. 



Whatever the air coming from the lungs contains that 

 was not in the air entering them, it has taken from the blood, 

 and what the air has lost it has given to the blood. The air 

 in the air vesicle is separated from the blood in the pulmonary 

 capillaries only by the thin wall of the air vesicle and the thin 

 capillary wall. Carbon dioxid, water, and other waste mat- 

 ters pass from the blood through this thin partition into the 

 air vesicle, to be sent out by later expiration. Oxygen from 

 the air in the vesicle passes through these layers into the 

 plasma, and most of it is quickly picked up by the colored 

 corpuscles. The colored corpuscles are the Carriers of Oxygen. 

 As has already been stated, the hemoglobin in the colored cor- 

 puscles has an affinity for oxygen. Hemoglobin is of a dark 

 color, and gives the dark color to the blood which enters the 

 lungs. When oxygen unites with the hemoglobin it forms 

 Oxy-hemoglobin, which is of a bright red color. Hence the 

 change in the color of the blood 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. 



Since the hemoglobin is dark, and gives the so-called " ve- 

 nous " blood its color, we might appropriately call the blood 

 that enters the lungs " hemoglobin blood." Since the hemo- 

 globin takes oxygen, becomes bright red, and gives the blood 

 its bright color as it leaves the lungs, no more suitable name 

 can be given to it than " oxy-hemoglobin blood." The only 

 good objection to these terms is their length ; but since they 

 are exact, while the commonly used terms are inexact, these, 



