PHAGOCYTIC ACTIVITY OF THE SPLEEN 445 



The outstanding features of the experiments are: 1) the definite 

 cycle which can be followed in the phagocytic activity of the 

 splenocytes, and, 2) the bone-marrow crisis occurring as a reaction 

 to the hemolysis of the pigeon corpuscles. 



In following the phagocytic history of the splenocytes, one 

 notes that the hemolysis of the pigeon blood is so rapid that few 

 of these cells are taken up intact. It is true that some are taken 

 up whole, but as dissolution proceeds, it is more and more the 

 fragments which are ingested by the splenocytes. At the one- 

 hour stage, the reaction has already begun, some of the inclusions 

 being recognizable as entire red blood-cells, others as amorphous 

 masses derived from the pigeon corpuscles. However, the 

 splenocytes are not greatly enlarged, and even by the end of 

 six hours, after an interval of several hours during which the 

 splenocytes have been surrounded by the disintegrating blood- 

 cells, their size is not conspicuously increased. Either the out- 

 put from the cells keeps pace with the intake or the phagocytic 

 process requires a number of hours for its completion. That 

 time is a necessary factor in the engulfment stage of phagocytosis 

 is also indicated in the action of the splenocytes toward the bone- 

 marrow cells. These first appear in the spleen at the two-hour 

 stage, and are abundant by the six-hour stage, but it is not until 

 the twelve-hour stage that any conspicuous number of these 

 cells are seen within the splenocytes. Thereafter the engulfing 

 process continues rapidly, and at sixteen hours, practically all 

 splenocytes are laden with these cells. 



As the result of the ingestion of myelocytes and polymorphonu- 

 clear cells, the size of the splenocytes greatly increases. An 

 average size is 25 X 20 n, but many are larger than this, and the 

 example shown in figure 5 measures 55 X 23.4 y.. In this cell 

 at least twenty bone-marrow cells can be counted within its 

 cytoplasm in a single 4 /j, section, so that one can judge that its 

 total capacity must be several times this number. 



After the stage of engulfment comes the digestion of the cells. 

 First the pseudo-eosinophilic granules lose their characteristic 

 staining capacity, although the nuclei still show their original 

 form. Gradually, however, the nuclei begin to shrink, and 



