THE BLOOD. 61 



throblasts or more frequently haematoblasts. The view is 

 held by many observers that these hsematoblasts are not the 

 lineal descendants of the nucleated red corpuscles of the 

 embryo, but are being regularly derived from the ordinary 

 white corpuscles of the blood found in the marrow. 



8. Length of Life of Red Corpuscles. That red cor- 

 puscles are being produced daily in great numbers is 

 evident from the fact that so many are destroyed in the 

 spleen and liver. The coloring matter of the bile is 

 derived from disintegrated red corpuscles, and the number 

 of corpuscles required to colof to such an extent the large 

 amount of bile daily eliminated exceeds calculation. It is, 

 of course, not possible to tell how long a red corpuscle will 

 retain its vitality and properly perform the functions ascribed 

 to it, but there are reasons to believe that the ordinary 

 length of life of such a corpuscle varies from three, to pos- 

 sibly not more than eight or ten weeks. To replace the 

 entire number of corpuscles in the body every two months 

 means a daily manufacture of them by the billions. In 

 fact, it seems a little like a fairy story to be told that for 

 every beat of the pulse nearly twenty millions of these 

 organisms die. Such a wholesale manufacture of them is 

 to be explained by the rapidity with which these haemato- 

 blasts are supposed to divide. The older view that red cor- 

 puscles were directly derived from the white ones, or from 

 the blood tablets, has been abandoned as not at all in 

 accordance with observed facts. The red or blood-forming 

 marrow is found in the extremities of most of the bones of 

 the trunk, and in the bones of the skull. It is interesting 

 that when the blood -formation process is very active the 

 yellow marrow itself may be changed into red through all 

 the bones. 



9. The Destruction of the Red Corpuscles. The fact 

 that corpuscles are short lived brings up naturally the ques- 

 tion as to the manner of their destruction and elimination. 

 As the pigments of the bile are derived from broken 

 down corpuscles there is no doubt that many of them are 



