42 VACCINE AND SERUM THERAPY. 



power, will retain this power on much greater dilution. They 

 have further found that in human beings, who are supposedly 

 in good health, the phagocytic power in concentrated serum will, 

 in some cases, diminish in proportion to the degree of dilution, 

 w r hile with the serum of other individuals, more rapid exhaustion 

 takes place. 



Moss has compared the opsonic index in various dilutions 

 of serum and has found that the index obtained in one dilution 

 is not proportional to that obtained in all the other dilutions. 



Walker's reports on the results obtained by the dilution of 

 serum differ from those obtained by Moss. Walker has found 

 that with many bacteria, undiluted normal serum will opsonize 

 so many bacteria in a heavy suspension of bacteria that the leu- 

 cocytes will contain so many microorganisms, that counting is 

 impossible. If the bacterial suspension be made less heavy fewer 

 bacteria will be taken up by the leucocytes, but under ' this 

 condition the serum will not be exhausted of its opsonin and 

 part will be lost in the estimation of the opsonic index. A 

 serum containing much less opsonin may opsonize just as many 

 bacteria in a light bacterial suspension as a serum containing 

 more opsonin. "When thin suspensions of bacteria for which 

 much opsonin exists in the serum are used it generally happens 

 that both the sera sensitize all the bacteria so that the work if 

 accurately done will produce equal phagocytic indices for both 

 in other terms, an opsonic index of unity regardless of the real 

 relation of the serum. Phagocytic indices proportional to the 

 sera tested may readily be obtained by diluting all the sera equally 

 to a sufficient degree, and using with these diluted sera a thick 

 bacterial suspension." For some bacteria as B. typhosus, cer- 

 tain strains of streptococci and tubercle bacilli, Walker does not 

 recommend the dilution of serum, while for staphylococci, 

 some strains of streptococci and tubercle bacilli and for B. coli 

 he does. 



Walker's views concerning the utilization of all the opsonin 

 capable of sensitizing the particular species of bacteria by the 

 use of heavy bacterial suspension and diluted sera, must be favor- 

 ably received. Before they can be accepted and followed it will, 

 however, be necessary to disprove the results of Moss and others 

 concerning the dilution of opsonin by the dilution of the serum. 



