218 



VETERINAEY PHYSIOLOGY 



they are formed in the red marrow of bone (fig. 105). 

 Marrow consists of a fine fibrous tissue with large blood 

 capillaries or sinuses running in it. In the fibrous tissues 

 are numerous fat cells (clear spaces b in fig. 105) and generally 

 a considerable number of multi-nucleated giant cells or 

 myelocytes (d). In addition to these are the young leucocytes, 

 leucoblasts (a.g.h.), and lastly young nucleated red cells, the 

 erythroblasts (c.f.). After haemorrhage, the formation of these 

 becomes unusually active, and may implicate parts of the 



FIG. 105. Section of Red Marrow of Bone, a, lymphocyte ; 6, fat cell ; c, 

 erythroblast ; d, giant cell ; e, erythrocyte ; /, erythroblast in mitosis ; 

 g, neutrophil myelocyte ; h, eosinophil myelocyte ; k, eosinophil 

 leucocyte ; I, polymorpho-nuclear leucocyte. 



marrow not generally concerned in the process, and hence 

 the red marrow may spread from the ends of the long bones, 

 where it is usually situated, towards the middle of the shaft. 

 The nuclei of the erythroblasts atrophy or are shed and the 

 cells escape into the blood stream. The red marrow has the 

 power of retaining the iron of disintegrated erythrocytes, 

 which are often found enclosed in large modified leucocytes 

 or phagocytes. The iron is often very abundant after a 

 destruction of erythrocytes. 



