On the Opsonic Action of the Stood Serum. 379 



" Experiments on the Nature of the Opsonic Action of the Blood 

 Serum." By WILLIAM BULLOCH, M.D., and E. E. ATKIN, B.A., 

 Bacteriological Laboratory, London Hospital, E. Communi- 

 cated by LEONARD HILL, M.B., F.K.S. Eeceived January 10, 

 Read January 19, 1905. 



In a series of simple and convincing experiments Wright and 

 Douglas* have shown that in phagocytosis so called, an important if not 

 a cardinal rdle is played by the body humors, whereby they act upon the 

 bacteria, thus rendering the latter an easy prey for the polynuclear 

 leucocytes. The demonstration of this opsonic action of the serum or 

 plasma was mainly brought about by testing separately and combined 

 the body humors and the corpuscles which had been washed in salt 

 solution. Contrary to general opinion, Wright and Douglas found that 

 the leucocytes were capable of engulfing microbes only when the latter 

 had been attacked by the serum or plasma. This attack on the microbe 

 does not lead to the death of the latter, as sera may manifest a marked 

 opsonic effect without being in the slightest degree bactericidal. 

 Wright and Douglas found that the opsonic substance was more or less 

 thermolabile, being destroyed in 10 to 15 minutes at a temperature of 

 60 to 65 C. In subsequent papers these authors have demonstrated 

 that there is a definite type of immunity in which the blood fluids 

 co-operate with the leucocytes to destroy the invading micro-organisms, 

 this being different from the antitoxic and bactericidal types of immunity 

 which have already been studied with completeness. 



Technique. The technique we have employed is that described by 

 Wright, and for the most part the experiments were made with living 

 cultures of Staphylococcus albus not more than 24 hours old. For accurate 

 and uniform results it is essential that the emulsions of the cultures 

 should be homogeneous, the bacteria being uniformly distributed and 

 separated from each other. This is best obtained by shaking, and the 

 subsequent application of the centrifuge. From their tendency to 

 group themselves into masses, certain strains of staphylococci are 

 unsuitable for determining the opsonic power of the serum. Where 

 different bacterial emulsions are compared with each other it is essential 

 that they should contain the same number of bacteria, a result best 

 obtained by counting and diluting as required.! The leucocytes were 

 obtained from the citrated blood of the authors and other human beings 

 or from rabbits. The sera used were either of human or animal origin 

 and were for the most part from normal individuals. 



In all cases the proportion of serum, bacteria, and corpuscles was 

 3:1:3. 



* ' Boy. Soc. Proc.,' vols. 72 and 73. 

 t See Wright, ' Lancet,' July 4, 1902. 



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