THE FLUIDS OF THE BODY 65 



loses that is to say, extrudes its nucleus. Others maintain 

 that the nucleated cells become irregular in form ; that haemo- 

 globin accumulates in the projecting portion of the cell ; that 

 this projecting portion breaks off as a non-nucleated corpuscle. 

 It would be indiscreet at the present time to pronounce in 

 favour of either of these reports, although the decision is of 

 theoretical importance. If the former account be true, red 

 blood-corpuscles are nucleated blood-cells which have lost their 

 nuclei. If the latter account be in accordance with fact, it is 

 hardly justifiable to regard them as cells. They are parts of 

 cells which finish their existence independently of the cell 

 body and nucleus to which they belong. As circumstantial 

 evidence, favouring the theory that cell division is normal 

 and the nucleus subsequently lost, may be pleaded the exist- 

 ence in marrow, and also in the embryonic liver and spleen, 

 of certain very peculiar cells. These cells have long been 

 known as giant cells, and all attempts at accounting for them 

 have broken down. They are relatively of immense size : 

 their diameter may be twenty times as great as that of a red 

 blood - corpuscle. Each contains a huge irregular, bulging 

 nucleus. Hence the cells are termed " megacaryocytes " (big- 

 nucleus cells). They must not be confounded with the poly- 

 caryocytes (cells with several nuclei), which eat up degrading 

 bone, although it must be confessed that megacaryocytes and 

 polycaryocytes appear to be genetically connected. It is sup- 

 posed that megacaryocytes consume the nuclei which red 

 corpuscles extrude during the process of their conversion from 

 nucleated cells. Traces of nuclei, or things which often look 

 like nuclei, are found in their body-substance. Their own over- 

 grown misformed nuclei appear to be the result of an excess 

 of nuclear food. It is certainly remarkable that megacaryo- 

 cytes are not found below mammals. They do not occur in 

 any animal in which red blood-corpuscles retain their nuclei. 

 Polycaryocytes are found in numbers in the bones of growing 

 birds. They are evidently scooping out bone from situations 

 in which it has to be displaced in order that the shape of 

 the bone as a whole may be changed. But there are no mega- 

 caryocytes in birds. On the other hand, megacaryocytes are 

 present in the liver, and later in the spleen, of mammals at the 

 periods when blood-formation is occurring most actively in 



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