INTERNAL RESPIRATION 159 



ing from no two different sets of capillaries is identical. 

 When all this meets in the right side of the heart and is sent 

 thence into the lungs it has a nearly uniform composition, 

 and needs only to receive O before it can supply the wants 

 of any particular tissue in the body. Arterial blood is also 

 more coagulable than venous. 



Internal Respiration. It has been said that the object of 

 external respiration and the transportation of O and CCte is 

 to make internal respiration possible. Oxygen, leaving the 

 alveoli in a manner already described, enters the blood and 

 at once combines with hemoglobin of the red corpuscles 

 to form oxyhemoglobin. A small portion of the O is used 

 up by the corpuscles in transit, with the production of CO2 

 and other metabolic materials 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 CO2 a result of their metabolic activity. The blood, 

 having thus given up its O, is changed in color, and carries 

 the CO2 back to the lungs to be exhaled. 



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

 respiration. Living tissue exposed to an atmosphere con- 

 taining O will consume O and exhale CO 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 CC)2, and O is directly necessary to this pro- 

 cess. But the amount of CCte 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 probable 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 CO2 is formed ; hence during activity comparatively 

 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 COz" (Reichert). 



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



