THE BLOOD 27 



about nine tenths of the solid matter of the red corpuscles and to it is 

 due the colors of the blood. When united with the oxygen it forms a 

 compound, called oxy 'hemoglobin, which has a bright red color; the 

 hemoglobin alone has a dark red color. These colors are the same as 

 those of the blood as it takes on and gives off oxygen. The stroma, 

 which forms only about one tenth of the solid matter of the corpuscles, 

 serves as a contrivance for holding the hemoglobin. The conditions 

 which cause the hemoglobin to unite with oxygen in the lungs and to 

 separate from it in the tissues, will be considered later (Chapter VIII). 



Disappearance and Origin of Red Corpuscles. The red corpuscles, 

 being cells without nuclei, are necessarily short-lived. It has been 

 estimated that during a period of one to two months, all the red 

 corpuscles in the body at a given time will have disappeared and their 

 places taken by new ones. The origin of new corpuscles, however, and 

 the manner of ridding the blood of old ones are problems that are not 

 as yet fully solved. The removal of the products of broken down 

 corpuscles is supposed to take place both in the liver and in the spleen. 1 



Regarding the origin of the red corpuscles, the evidence now seems 

 conclusive that large numbers of them are formed in the red marrow of 

 the bones. The red marrow is located in what is known as the spongy 

 substance of the bones (Chapter XIV) and consists, to a large extent, 

 of cells somewhat like the red corpuscles, but differing from them in 

 having nuclei. These appear to be constantly in a state of repro- 

 duction. The blood, flowing through the minute cavities containing 

 these cells, carries those that have been loosened out into the blood 

 stream. Nuclei appear in the red corpuscles at the time of their forma- 

 tion, but these quickly separate and, according to some authorities, 

 form the blood platelets. 



White Corpuscles. The white corpuscles, or leucocytes, 

 are cells of a general spherical shape, each containing one, 

 two, or more nuclei. They are much less numerous than 

 the red, there being on the average only one white cor- 



1 The coloring matter of the bile consists of compounds formed by the breaking 

 down of the hemoglobin ; the spleen contains many large cells that seem to 

 have the power first of "engulfing" and later of decomposing red corpuscles. A 

 further evidence that the spleen aids in the removal of worn-out corpuscles is 

 found in the fact that during diseases that cause a destruction of the red corpuscles, 

 such as the different forms of malaria, the spleen becomes enlarged. 



