THE WHITE BLOOU CELLS 207 



concentration of the blood and an apparent increase in the number 

 of its corpuscles. The number of red blood corpuscles in the female 



b 



FIG. 222. THREE NU- 

 CLEATED RED BLOOD 

 CELLS (ERYTHRO- 



CYTES) FROM THE 



FIG. 221. FIVE NUCLEATED RED CELLS MARROW OF A Hu- 



(ERYTHROCYTES) FROM THE BLOOD OF MAN RJB. 



A FROG. 



Eosin - methylene 



Eosin-methylene blue. Hasting's blue. Nocht method, 



method. X 1200. X 1200. 



is slightly less than in the male, about 4,500,000 per cubic millimeter. 

 The average life of an erythroplastid is approximatety 30 days (Ashby; 

 Journ. Exp. Med., vol. 29, 1918). 



THE WHITE BLOOD CELLS 



Under leukocytes are grouped the following types: (1) lymphocytes; 

 (2) non-granular or mononuclear leukocytes and (3) granular leukocytes 

 granulocytes. These are all nucleated elements. Leukocytes lack a 

 cell membrane; all are phagocytic, especially the neutrophils; they aver- 

 age about 8,000 to a cubic millimeter of blood. 



Lymphocytes. The lymphocytes are perhaps the least differentiated 

 blood element. They are of two main varieties, large and small, between 

 which are intergrades. The small lymphocyte is about the size of an 

 erythroplastid ; its nucleus is a dense, deeply chromatic spheroidal body ; 

 it has a very thin shell of very finely granular or non-granular faintly 

 basophilic cytoplasm. The large lymphocyte (12 to 15 /* ) differs from 

 the small, both in somewhat larger size of nucleus and slightly wider 

 shell of cytoplasm. The simplest and more than likely the correct con- 

 ception of the relationship of large to small lymphocytes is one of growth ; 

 that is, a large lymphocyte is a fully grown small lymphocyte, a small 

 lymphocyte is a daughter-cell of a large lymphocyte. They constitute 

 about 20 per cent, of the total white blood cell content. They are the 



