THEORIES OF IMMUNITY. 



and summarized by Ritchie, I. c, p. 283 et seq.). 

 "The fact has long been known that in many in- 

 fectious conditions the number of leucocytes in 

 the circulating blood is increased, but these 

 observers were the ones to demonstrate the 

 pronounced genninative activity which occurs in 

 any infection, in the precursors of these cells. 

 With regard to the leucocytic phagocytosis, 

 Muir has shown both experimentally on animals 

 and by observations on man, that in infections 

 where there is a polymorphonuclear leucocytosis, 

 not only is there evidence of an active division of 

 the parent cell in the bone marrow, but so active 

 is this process that the red marrow increases in 

 amount and encroaches on the yellow. In a 

 case of pneumonia, for instance, a few days after 

 the commencement of the disease the red mar- 

 row may have increased so as to occupy a 

 seventh part of the whole medullary cavity of 

 the femur. Not only, however, does prolifera- 

 tion occur in the site of formation of such an 

 important class of cells as the polymorphonu- 

 clear leucocytes, but Muir has also shown that 

 proliferation occurs during some infections in 

 such fixed cells as those lining the sinuses of 



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