LBUCOCYTB8 KXAMINED. 47 



investigators have obtained markedly different phagocytic indices 

 on the same slide. The writer has reported work showing that 

 there is not always agreement between results obtained by count- 

 ing the bacteria in 100 and 200 polynuclear leucocytes on the 

 same slide. Bolduan, Moss, Cole, Jeans and Sellards, Simon and 

 others have published 'results showing striking differences in the 

 counts obtained in 50, 100, 200 and more cells. Bolduan supposes 

 that counting the number of bacteria ingested by 100 or 150 cells 

 will give a fairly correct average. Potter, Dittman, and Bradley 

 believe counts in 100 cells suffice in most cases. Moss, in an effort 

 to determine how many leucocytes must be examined, has de- 

 cided that after counting the bacteria in three hundred cells there 

 is still an error of ten per cent ; and when 50 cells only are counted 

 his experiments show a variation of from .8 per cent to 30 per 

 cent. Most investigators determine the number of bacteria taken 

 up by at least 100 leucocytes. 



Large numbers of leucocytes must be examined because of 

 the variability of the number of bacteria taken up by the indi- 

 vidual leucocytes. Cells which are apparently normal as far as 

 can be determined by staining and which may contain an average 

 of from 5 to 8 bacteria per leucocyte, will phagocyte from 20 to 

 30 microorganisms at a maximum while other leucocytes may 

 take up none. This difference in the number of bacteria taken 

 up by individual leucocytes has been supposed to be due to the 

 leucocytes themselves and to clumps in the bacterial emulsion. 

 Walker has suggested that the leucocytes be kept constantly at a 

 temperature of 37 C., and that they be well mixed after incuba- 

 tion with serum and bacterial emulsion. Undoubtedly all in- 

 vestigators have mixed the leucocytes, bacteria and serum well 

 after incubation and before making the spreads to be examined. 

 This procedure, however, does not overcome the differences in 

 numbers of bacteria per leucocyte, as is shown in Walker's tables, 

 in which the variations in numbers of bacteria ingested range 

 from 1 to 15, 2 to 16, 1 to 17, and 4 to 16 in four sets of 25 leuco- 

 cytes examined. It cannot be concluded from this that there is 

 a uniformity of phagocytosis, although Walker's tables do show 

 a uniformity of phagocytic index in groups as small as 25 leuco- 

 cytes. It is evident, however, that if 25 leucocytes only were 

 to be examined, the opsonologist might, after he had examined 



