CHICKEN BONE MARROW IN PLASMA MEDIUM 101 



The large mononuclear lymphocytes of the type occurring in 

 the flowing blood, present in great numbers after the first day of 

 incubation, form now and then fine granules, but undergo no 

 further development into myelocytes. They lose their nuclear 

 chromatin, and their plasma becomes honeycombed and finely 

 vacuolized, and they finally leave as the only trace of their ex- 

 istence faint shadows in the plasma clot. 



The so-called fat cells of the bone marrow flatten out; the 

 big fat globules divide into smaller droplets; their plasma either 

 vacuolizes and forms long needle-like projections, or fibroblast- 

 like cells with a central nucleus and honeycombed plasma. The 

 first cell type is phagocytic. These cells represent 'Riesenzel- 

 len' in the first period of the tissue culture growth. Not all 

 cells of this type are transformed into fibroblasts or 'Riesenzel- 

 len.' Some fat cells disintegrate filling the culture medium with 

 degenerating fat particles. Now and then the nucleus, with a 

 small amount of cytoplasm separates from the dying 'fat cell' 

 and a young 'rejuvenated' cell of fat cell character appears. The 

 so-called fat cells combine the first regressive period of bone 

 marrow growth with the second of more progressive character. 

 Some undergo destruction, some survive, later assuming Foot's 

 cell culture type. 



From the first day of incubation, connective tissue cells of 

 elongated shape with very fine pointed projections migrate into 

 the plasma clot. They store fine droplets of fat and partially 

 vacuolize. They are also found in the second period of growth 

 in the tissue culture. 



The second period begins ^\dth the loosening up of the cells 

 around the network of the bone marrow; the smaller, or larger 

 basophil cells, with vesicular nucleus migrate into the surround- 

 ing plasma and the network sends new cells into the plasma clot 

 till it is utterly devoid of cell forms. These cells represent an 

 intermediate type between the 'histiotype Wanderzellen' (Dant- 

 schakoff, '09) and the embryonic mesenchyme cell. They do not 

 resemble in all details the large nononuclear lymphocyte of the 

 blood. They move into the surrounding plama, send out pene- 

 trating needle- and bristle-like projections; divide into phago- 



