XIV 



THE LYMPH 



5:',5 



those that issue from the hone are furnished with an extraordinary 

 number of them. 



The cells contained in the lacimar system of the marrow are 

 quite characteristic of this tissue. Among them four principal 

 kinds can be distinguished: leucocytes, megacaryocyfces (giant- 

 cells), erythroblasts, erythrocytes. 



The leiicociit?* of bone marrow comprise many varieties, which 



!'!. . -">-. Leucocytes from do<('s bone marrow, dry preparation. ", /, Younj; leucocytes ( or 

 lymphocytes, \vitli giant nuclei and little cytoplasm ; c, d, medullary cells or adult leucocytes 

 with reniform and polymorphous nuclei ; c, leucocytes umli-r^oinjj mitotic division. 



a single 



probably represent different states of development of 

 cellular type, since there are always numerous transitional forms 

 from the one to the other variety. The differences lie in tbe 

 dimensions, form of nucleus, 

 and character of cytoplasm. 

 The youngest (lymphocytes) 

 are the smallest, owing par- 

 ticularly to the paucity of pro- 

 toplasm around the nucleus ; 

 the disc -shaped nucleus is 

 rich in chrdmatin. The rnoiv 

 adult (medullary cells) are 

 larger, with a reniform 

 polymorphous, sometimes 

 multiple nucleus, poor in 

 chromatin. These are not 

 found in normal circulating 

 blood, only in states of leu- 

 caemia (Fig. 2") 2). 



Howell's megacaryocytes 

 were discovered in 1869 by 

 Bizzozero, who called them giant cells with a budding central 

 nucleus. They have an average diameter of 25-45 //. Their 

 nucleus is very variable in form, often horseshoe-shaped. Heiden- 

 hain distinguishes several types or varieties according to the different 

 degree of differentiation of the cytoplasm, which is sometimes 

 arranged in three concentric zones (Fig. 253). Bizzozero had 



-"'3. Megacaryocyte of l>oiie marrow, in which 



nucleus 



from the cytoplasm, divided into three 

 /ones. (Hcidenhain.) 



be distinguished 

 concentric 



already suggested that the 



giant 



cells were derived from the 



leucocytes of bone marrow, since there is a whole series of forms 



