506 APPLIED BIOLOGY 



absorbing oxygen from air in the air-chambers through the 

 delicate walls of the chambers and into adjoining blood- 

 capillaries. >*;, 



We must guard against the common error of supposing 

 that venous blood coming back to the lungs from all other 

 organs is devoid of oxygen. The fact is that every 100 cc. 

 of venous blood coming to the lungs has about 10 cc. of 

 oxygen dissolved in the blood, and when it leaves as arterial 

 blood it has about 20 cc. In other words, the amount of 

 oxygen is doubled in arterial blood. This additional oxygen 

 becomes combined with the haemoglobin in the red cor- 

 puscles, and results in the change of color. Blood with- 

 out the red cells could not contain so much oxygen, and 

 hence vertebrates have a great advantage over the lower 

 animals. 



431. Distribution of Oxygen to Cells. Blood carrying 

 oxygen received in the lungs passes from the left auricle to 

 the left ventricle of the heart, and thence to all the organs ex- 

 cept the lungs. As the blood flows through the capillaries in 

 organs, some of its oxygen is absorbed by near-by cells and 

 some by the lymph, which distributes it to cells that are 

 distant from blood-capillaries. Recall the statement that all 

 living cells are continually using oxygen, and it is obvious 

 that they as constantly must demand a fresh supply. If 

 the blood were to stop flowing for even a short time, the 

 available oxygen in the lymph and blood in every organ 

 would soon be used by the oxidation going on in protoplasm ; 

 and the result would be asphyxiation of the cells. But under 

 normal conditions the flow of blood is so rapid that only 

 approximately one-half of its contained oxygen is extracted 

 while it flows from the arteries through the capillaries into 

 the veins. ; Hence venous blood returning to the lungs has 

 about one-half the oxygen of the arterial blood leaving the 

 lungs. 



