OXYGEN AND CARBON DIOXIDE IN THE TISSUES 159 



make internal respiration possible. Oxygen, leaving the alveoli 

 in a manner already described, enters the blood and at once com- 

 bines with hemoglobin of the red corpuscles to form oxyhemo- 

 globin. A small portion of the O is used up by the corpuscles in 

 transit, with the production of CO 2 and other metabolic mate- 

 rials the corpuscles requiring O in their metabolism just as do 

 other cells. But by far the largest portion is carried to the 

 capillaries, where it is taken up by the cells. At the same time 

 the cells give up to the blood CO., a result of their metabolic 

 activity. The blood, having thus given up its O, is changed in 

 color, and carries the CO ? back to the lungs to be exhaled. 



To furnish O and to remove CO 2 is the only object of respira- 

 tion. Living tissue exposed to an atmosphere containing O will 

 consume O and exhale CO 2 even if no blood be circulating through 

 it. The exact manner in which a cell uses O is not apparent. 

 It is evidently an oxidation process which produces CO 2 , and O 

 is directly necessary to this process. But the amount of CO 2 

 produced in any given time may not correspond to the amount of 

 O consumed in that time ; it may be greater or less. " It is prob- 

 able that during rest O is utilized to some extent in oxidations 

 which are not at once carried to their final stage and in which 

 relatively little CO 2 is formed; hence during activity compara- 

 tively little O is required to cause a final disintegration of the 

 now partially broken down substances, and thus to give rise to 

 a relatively large formation of CO 2 " (Reichert). 



The absorption of O is to be looked upon as a part of the 

 nutritive process just as the absorption of proteid, e. g., and CO 2 

 as one of the products of destructive metabolism just as urea. 

 There is small probability that the O unites directly with the 

 carbon of any of the food stuffs although this is the final 

 result. 



Interchange of Oxygen and Carbon Dioxide in the Tis- 

 sues. Here application of the principles governing the inter- 

 change of these gases in the lungs applies. It is found that 



