PHAGOCYTIC ACTIVITY OF THE SPLEEN 443 



Eight and one-half hours. The appearance at this stage is 

 similar to the preceding. There is an abundance of myelocytes 

 and of pseudo-eosinophiles. The splenocytes usually contain 

 numerous small inclusions of hemosiderin and are not very 

 conspicuous. 



Twelve hours. The splenocytes are now beginning to show 

 inclusions of nucleated cells, in addition to the blood pigment 

 derived from the pigeon red blood corpuscles. This is the last 

 stage at which hemoglobinuria was noted, and apparently the 

 pigeon blood has for the most part been disposed of. The 

 phagocytosis of the bone-marrow cells by the splenocytes is now 

 commencing, and shows most strikingly at the next stage. 



Sixteen hours. At this period, one can readily discern the 

 splenocytes with a low power of the microscope, by reason of 

 their increased size. In figure 4 is shown a characteristic field. 

 Every splenocyte contains a number of nucleated cells, both 

 polymorphonuclears and myelocytes with their granules still 

 staining characteristically. An average size is 25 X 20 n, in 

 contrast to their previous size of 16 X 10 fi. A large one, shown 

 in figure 5, measures 55 X 23.4 /*, and in single 4 n section, twenty 

 cells can be counted within its cytoplasm. This period evidently 

 shows the splenocytes at the height of their phagocytic activity 

 toward the animal's own bone-marrow cells. There are scattered 

 extracellular masses of hemosiderin. The polymorphonuclears 

 are still abundant, but the myelocytes are apparently not so 

 numerous, and this is probably due to the activity of the spleno- 

 cytes. At this period there was no discernible hemoglobinuria. 

 Tests for iron showed this to be present in many endothelial cells, 

 but in much greater amounts within splenocytes. 



Twenty-one hours. The splenocytes are now smaller in size, 

 and accordingly less conspicuous than at the preceding period. 

 Their diminution in size is to be associated with the shrinkage 

 of their cellular inclusions. While in some of the splenocytes, 

 the ingested cells show both nuclei and granules stained character- 

 istically, in others, only the nuclei of the ingested cells remain 

 recognizable, and apparently the red-staining substance has been 

 altered, probably by digestive ferments within the cell. Some 



