Electron Microscopy of the Lymphocyte 65 



of the other cell types, regardless of their stage of development. In normal 

 peripheral blood, although there are cells that cannot be positively identified 

 as either lymphocyte or monocyte, many cells are present with lymphocytic 

 characteristics that indubitably connect them with the parent lymphoblast. 

 The few plasma cells in normal peripheral blood are, in electron micro- 

 scopic morphology, much closer to monocytes than to lymphocytes, and 

 "monocyte-plasma cell intergrades" have been observed. The weight of the 

 electron microscopic evidence now available argues strongly that, apart from 

 all other developmental series of blood cells and their derivatives, the lym- 

 phocytic series stands alone. 



ACKNOWLEDGE EN TS 



Grateful acknowledgment is made to Mr. Gordon D. Moore lor thin sectioning, 

 to Mr. Robert E. Druce for microscope maintenance, and to Mr. Max R. Clev- 

 enger for photographic and general technical assistance. 



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