THE BLOOD ' 223 



Hemoglobin can be dissolved in water or in plasma but 

 it is normally retained in the corpuscles through the 

 agency of their other components. The structure 

 involved is not well understood. 



It is hemoglobin which confers on the corpuscles 

 their power to unite with oxygen. The union takes 

 place in the lungs and a temporary compound is formed 

 which is called oxyhemoglobin. This is bright red. As 

 the blood flows through active tissues close to cells 

 which are consuming oxygen the corpuscles yield more 

 or less of the oxygen which they have just now attached. 

 In so far as they do this their oxyhemoglobin is changed 

 to what is spoken of as reduced hemoglobin. This is 

 blue-black and the more of it there is present the darker 

 the blood. It is not usual for any portion of the blood 

 to give up all its oxygen and so contain nothing but 

 reduced hemoglobin. This may happen in suffocation 

 or, locally, in intense muscular activity. The details 

 are better taken up in the discussion of respiration. 



The History of the Red Corpuscle. It has been said 

 that red corpuscles are not cells in the full sense of that 

 term. It is a question whether we ought to consider 

 them to be alive; perhaps we gain nothing by assuming 

 that they are so. But each corpuscle is probably to be 

 regarded as a modified or degenerate cell and its history 

 is fairly clear. It had its origin in an unexpected 

 locality, the red marrow of the bones. We must make 

 a distinction between this type of marrow and the more 

 conspicuous white or yellow marrow which is found in 

 the hollow shafts of such bones as those in the arms and 

 legs. White marrow is largely fat. The red marrow is 

 found in minute spaces in the expanded ends of the long 

 bones, for example, about the knees and elbows. 



Microscopic examination and chemical tests of the 

 red marrow show that it is composed of cells which are 

 rich in hemoglobin. The blood flows among these cells 

 and comes into relatively direct contact with them, since it 

 is not here confined in definite vessels. Those cells which 



