392 



INFLUENCE OF THE DILUTION OF SERUM, 



were tested in the same manner as in the previous experiment. 

 The phagocytic indices were 19*4, 15-7, and 11"7 respectively. 



Days since Race was isolated. 



Serum 



,, diluted ^ 



,. i 



,, i 



'» 5! tV 



Average. 



1-00 

 0-74 

 0-56 

 0-50 

 0-40 



The average curve falls very regularly, and is virtually a 

 straight line hetween unity and the one-eighth dilution. The 

 individual curves run close together to the -| dilution, when the 

 oldest race shows a more pronounced rise than the others. Still 

 there is nothing to account for the observed irregularities in the 

 curves from time to time. 



Bacteria which have been heated nnd partly freed from anti- 

 opsonin by washing, show a greater facility for being ingested 

 by the phagocytes at the half- and quarter-dilution compared 

 with the unwashed bacteria. In the following, the bacteria 

 were suspended in saline, and heated at 60° for an hour; then 

 sedimented in the centrifuge, and finally suspended in saline. 

 Bacteria suspended in the usual way were used for comparison. 

 The indices with undiluted serum were 13'7and 17-7 respectively^ 



The injiuence of the scdine. — Dean, in his work upon the effect 

 of dilution upon the opsonic curve, makes no mention of strength 



