298 ANATOMY AND PHYSIOLOGY FOR NURSES 



between the oxygen of the atmosphere and the blood in 

 the lungs is one of a semimechanical character, very 

 similar to that previously existing between the oxygen and 

 the nitrogen in the atmosphere. 



Oxygen does combine with the blood in the lungs; this 

 is shown by the change it produces in the color and con- 

 sistence of this fluid; these changes have been seen to 

 take place in experiments exposing venous blood to the 

 action of oxygen outside the body. It must, however, 

 be evident that this combination occurs with the mass of 

 the blood, and not between this element and the individual 

 constituents of the vital fluid. In the latter case the effects 

 must of necessity be quite different from those that take 

 place in the lungs. 



It is a fact, which appears to be self-evident, that the 

 combustion of oxygen and carbon, whereby carbon dioxid 

 is formed, takes place after the oxygen is carried by the 

 circulation into the capillary vessels, for it is here that the 

 peculiar effects of the workings of this process are evinced. 

 It is in this part of its passage that the blood undergoes its 

 remarkable change, and it is here that it acquires its dark 

 purple color; it is at this time, too, that carbon dioxid, 

 which is the evidence of combustion, or the chemic unit 

 of oxygen and carbon, is present. If the point of origin 

 of the process of oxidation, here said to be the cause of 

 the evolution of animal heat, is traced, it will be found that 

 instead of the phenomenon occurring entirely within the 

 lungs, it takes place through the system in every tissue 

 and organ of the entire body. 



In the circulation of the blood we find that two import- 

 ant changes occur; these might be said to take place at 

 entirely opposite points. By one of these changes the 

 color of the blood is altered to a marked red ; by the other, 

 to a dark or purple red; and it is this last-named change, 

 and not the first, that indicates the specific office of the 



