CHANGE IN COLOR OF THE BLOOD. 455 



ed by the pulmonary vein with the bright red color of arterial 

 blood. When the artificial respiration is interrupted, the 

 blood passes through the lungs without change. 1 In expos- 

 ing the thoracic organs, and keeping up artificial respiration, 

 repeating the celebrated experiment of Robert Hooke, made 

 before the Royal Society in 1664, we can see through the 

 thin walls of the auricles the red color of the blood on the 

 left side contrasting with the dark venous blood on the right. 



Since the discovery of oxygen, it has been ascertained 

 that this is the only constituent of the air which is capable 

 of arterializing the blood. Priestley showed that venous 

 blood is not changed in color by nitrogen, hydrogen, or car- 

 bonic acid ; while all these gases, by displacing oxygen, will 

 change the arterial blood, from red to black. 2 



The elements of the blood which absorb the greater part 

 of the oxygen are the red corpuscles. While the plasma will 

 absorb, perhaps, twice as much gas as pure water, it has been 

 shown by Magnus and Gay-Lussac that the corpuscles will 

 absorb from ten to thirteen times as much. 3 By some the 

 proportion is put much higher. The red corpuscles may be 

 considered as the respiratory elements of the blood. It is 



1 This demonstration is very striking, especially if we use a syringe with a 

 double nozzle, one point secured in the pulmonary artery, and the other simply 

 carrying the blood by a rubber tube into a glass vessel. Eeceiving the blood 

 which passes through the lungs, and that which simply passes through the tube, 

 into two tall glass vessels, the one is of a bright red, and the other retains its 

 dark color. In preparing for the experiment it is necessary, immediately after 

 removing the lungs from the animal, to inject them with a little defibrinated blood, 

 so as to remove the coagulating blood from the pulmonary capillaries, which would 

 otherwise become obstructed. The injection should be made gently and gradually, 

 to avoid extravasation. Defibrinated ox-blood may be used. The most conven- 

 ient way to secure the canulse in the vessels is to push them into the pulmonary 

 artery through the right ventricle, and into the pulmonary vein through the left 

 auricle. 



2 Carbonic oxide and nitrous oxide have a strong affinity for the blood-corpus- 

 cles, and become fixed in them, the former giving the blood a vivid red color. 

 Sugar and many salts will also redden venous blood. These agents, however, do 

 iiot impart the physiological properties of arterial blood. 



3 ROBIN and VERDEIL, op. tit., tome i., p. 32. 



