THE OPSONIC EXPERIMENT 501 



The opsonic index is thus : 



(log a n - log y n ) unknown 

 (log ao - log y ) normal 



In this calculation ordinary logarithms to base 10 may be used. 



In Table I. a close agreement between observed and calcu- 

 lated figures is shown. The first column gives the group 

 number — /.^.containing o, 1, . . ., etc. Observed and calculated 

 figures of numbers of cells in each group are tabulated side by 

 side in the other columns. The first three experiments are 

 from Fleming (quoted by Greenwood, Biometrica) ; the latter 

 two are by Harvey {Biometrica, vii. p. 64). 



Table I. 



In the foregoing argument two factors have been neglected 

 which may operate during an experiment. In the first place, it 

 is very probable that the faculty of ingestion will diminish as 

 the leucocyte fills up ; and in the second, if under the con- 

 ditions of experiment sedimentation be permitted, and if there be 

 a difference in the specific gravities of micro-organism and 

 leucocyte, then the engorged leucocyte may move into a thicker 

 swarm. These two factors will operate in contrary directions, 

 the former causing a decreased appetite and the latter an 

 apparent increase of appetite. I have seen no indication of 

 decreased appetite in the figures which I have examined, but 

 comparison between the column with heading " Mean ob- 

 served" and the column "z" (mean calculated) in Table II., 



