384 



THE INFLUENCE OF THE DILUTION OF SERUM 

 UPON THE PHAGOCYTIC INDEX. 



By R. Greig-Smith, D.Sc, Maclsay Bacteriologist to thk 



SOCIP^TY. 



(With eight text-figs.) 



When normal serum is progressively diluted with physiological 

 salt solution, the opsonic activity is found to rise with tlie 

 dilution to a certain point and Ihen fall. This was noted by 

 Wright and Douglas,"^ and was confirmed during my work.f 

 DeanJ showed later that the phenomenon was probably caused 

 by two factors, one of which causes a sharp rise from infinity to 

 anoint at the quarter dilution when another factor comes into 

 play and, retarding the rapid rise, causes a fall in the curve from 

 the half dilution to the undiluted serum. In my o\vn experiment 

 this point agreed with the J dilfition, and, in Wright and Douglas's 

 experiment, it was probably at the yV As Dean has taken the 

 average of a greater number of experiments, his number is more 

 trustworthy, although it must be remembered that he probably 

 mMde his tests by the more modern method of .using the serum 

 and suspensions of corpuscles and bacteria in the ratio of 1:1:1, 

 while both Wright and I used the older ratio of 3:3:1. The 

 greater proportion of serum to saline might cause the differences 

 between the points when the depressing action of the serum 

 appears. 



In endeavouring to account for the behaviour of the serum 

 upon the dilution, much might be gained by remembering that 

 opsonisation, while possibly not identical with, may still be' 

 closel}' related to agglutination. In a former paper I showed 

 that they were probably identical; and recently Weil,|| in a 



* Proc. Roy. Soc. 73, (1903), No. 483, p. 364. 



t These Proceedings, 1905, p. 563. 



: Proc. Pvoy. Soc 79, (1907), No.B 533, p.401. 



11 Centrlb. fiir Bakt. Ref. 42(1908), p.34o. 



