74 RHODA ERDMANN 



elements behave differently in the tissue cultures and may, 

 after having undergone important changes in the plasma, offer 

 some difficulties in interpretation. 



The only observations of normal chicken bone marrow in 

 plasma are those made by Foot '12 and '13. In the first series 

 of experiments he studied especially the behavior of the fatty 

 elements of chicken bone marrow, recording the following re- 

 sults. Six hours after implantation numerous cells leave the 

 tissue center. They form rays of cells liquefying the plasma. 

 These rays are formed by polymorphous leucocytes wdth eosin- 

 ophile granules and by ''eine Art von mononuklearen basophilen 

 Zellen" (p. 450). Foot gives the latter the name of X cells; 

 they are the most important and they contain only fat accord- 

 ing to his observations of 1912. They form, he says in 1912, 

 the bulk of all cells migrating into the surrounding plasma. 

 These X cells, the origin of which Foot tries to elucidate, are 

 true phagocytes They include small fatty droplets and other 

 particles which are dispersed in the cytoplasm. On the fourth 

 day, these cells, after having been enlarged by the amount of 

 fat which they have taken up during the first three days in the 

 culture, form either syncytial masses or a widely spread network 

 of anastomosing cells. The former may divide, after having 

 lost most of their fatty granules, and form the final 'ruhende 

 X Zelle' (Foot '12, fig. 8, pi. 22) : or the latter, after having been 

 highly vacuolized, as stated by Foot '12, may form fibrils 

 (fig. 18, pi. 22). If these X cells do not form resting X cells or 

 cells which produce fibrils, they take the shape of 'Riesenzellen.' 

 These ' Riesenzellen' are not identical, in Foot's opinion, with 

 the 'giant' cells of the normal bone marrow. They are repre- 

 sented in his figures 11, 16, 17, 19. They are only X cells which 

 have fused together, form no fibrils, and may later break up in 

 small cells (figs. 12 to 14), which have generally one nucleus. 

 ''Das Ergebnis der Aufteilung der Riesenzellen ist sozusagen eine 

 neue Zellrasse" (p. 460) — cells adapted to the condition of the 

 medium. 



Foot believes that the X cells are transformed cells of the 

 'mesenchyme' and "Zwar indifferent gewordene Mesenchymzel- 



