THE BLOOD CELL 93 



methylene blue or neutral red, an otherwise invisible structure appears 

 in some cells in the form of coarse granular particles or threads, which 

 give a reticulated appearance to the corpuscles. These reticulated cells 

 are more abundant in infants' blood and in patients suffering with se- 

 vere anemia or hemolytic jaundice than in normal blood, and may be 

 taken as evidence of the youth of the red cell and not as a degenera- 

 tive process. Since the number of the reticulated cells that are present 

 in the blood is more or less directly proportional to the hemopoietic 

 activities of the bone marrow, enumeration of the reticulated cells is 

 of clinical importance in anemias. In conditions in which animals have 

 been made plethoric by the transfusion of blood,- it has been found that 

 the number of reticulated cells is decreased; the bone marrow of these 

 animals also shows a marked reduction in reticulated erythroblasts. 

 The diminished rate of blood cell formation sometimes noted after blood 

 transfusions may be explained by assuming that the stimulus which 

 awakens the formation of red cells in the bone marrow is absent or 

 made subnormal on the injection of red cells into the blood, and thus 

 the formation of red cells is depressed. Small transfusions are there- 

 fore preferable to large ones in cases in which the rate of blood forma- 

 tion is greatly impaired. By means of living cultures of red bone mar- 

 row the different stages of the development of the normoblasts into 

 true red corpuscles may be studied (Tower and Herm 5 ). Some evidence 

 has been gathered from such studies which points to the conclusion that 

 in place of the red cells being cells which have lost their nucleus, as is 

 the current teaching, they are rather cells which develop as a nuclear 

 bud and escape into the circulation as true red cells.. The nucleated 

 red cell and the red nucleated corpuscle of the bird are the product of 

 intranuclear activity and are morphologically identical. 



Rates of Regeneration of Erythrocytes 



Microscopic examination of the blood during rapid regeneration of 

 red cells shows the presence of nucleated forms. Nucleated red cells 

 in the blood have therefore been taken as an inevitable feature of rapid 

 blood regeneration. The evidence upon which this belief depends, 

 however, is hardly complete, since changes in the manner of red blood 

 cell formation may be responsible for the nucleated forms. The red 

 bone marrow is considered the seat of red cell formation, and it is true 

 that an abnormal increase in the red bone marrow usually accompanies 

 increased red cell formation. The nature of the stimulus which brings 

 about the new. formation of red cells is not understood. Oxygen w r ant 

 may be an important factor, since we find the presence of an abnormally 

 large number of red cells in conditions where there is a scarcity of 



