CHICKEN BONE MARROW IN PLASMA MEDIUM 75 



len" (p. 4()G). He reasons as follows: Because these cells have 

 the potentiality of forming fibrils they must belong to those 

 cells which can form connective tissue, and therefore these X 

 cells without any intermediate stages take their origin from 

 mesenchymal or endothelial cells. In a postscript to this paper 

 he changes his opinion entirely and says (p. 475): "Was die 

 Herkunft der X Zellen betrifft, so scheint es als ob die Haupt- 

 masse derselben entweder direkt oder indirekt von den lympho- 

 cytaren oder myeloblastischen Elementen des Knochenmarkes 

 abstammte," promising to give the reasons for this change of 

 opinion in his second communication. 



After a careful study of Foot's second publication ('13), 

 which is rather difficult to understand because he does not very 

 often connect his first publication with the second, I restate in 

 his own words his revised opinion of the origin of those cells which 

 form X cells ('13, pp. 46-47). ''The deductions as to the trans- 

 formation of the lymphocytes from one form to another, which 

 form the basis of the following descriptions, were made from 

 the observation of transition forms. The later transformations 

 of these cells into forms resembling fat and giant cells or cells 

 of the connective tissue have been considered in my pre- 

 vious article." So it appears that the so-called X cells of this 

 author ('12) — the name does not often appear in the paper of 

 1913 — are not directly transformed cells of the mesenchymal 

 type but are said to be of lymphocytic origin. He observes 

 that as early as three hours after implantation of the bone 

 marrow a considerable number of microlymphocytes emigrate 

 from the tissue particle. Their transformation occurs in the 

 following way: 



The small microlymphocytes are first transformed into ma- 

 crolymphocytes, later into large mononuclear forms, then into 

 myelocytes. At last the polymorphonuclear leucocytes appear, 

 after having undergone difi"erent changes in the form and struc- 

 ture of the nucleus. The nucleus is at first horseshoe-shaped, 

 later polymorphonuclear and even polynuclear. Finally the 

 cells, by rounding off and dechromatization of the nucleus 

 coincident with the rarification and a change in the staining 



