VI. SEROLOGICAL REACTIONS 647 



value of the standard serum, B the equivalent end point of the un- 

 known, and B' the equivalent end point of the standard serum. 



Complement Fixation (Goodner and Horsfall 538 ) 



As expressed by Goodner and Horsfall, "Complement is not fixed by 

 immune aggregates resulting from the interaction of pneumococcus cap- 

 sular polysaccharide and type-specific immune horse serum, although 

 under proper conditions the substitution of immune rabbit serum gives 

 positive results." The materials and methods used by these authors are 

 as follows: Fresh guinea pig serum (complement), a 5 per cent suspen- 

 sion of washed sheep red blood cells, and the serum of a rabbit im- 

 munized with sheep red blood cells (amboceptor). Each reagent is used 

 in a volume of 0.5 cc. The amboceptor is titrated with excess of comple- 

 ment and so diluted that 0.5 cc. contains 2 units. The complement is 

 titrated against 2 units of amboceptor. The final volume in each tube of 

 the titrations is 1.5 cc. The majority of the experiments were carried 

 out with the acetyl form of Type I pneumococcus capsular polysaccha- 

 ride. 



For further details of the tests the reader is referred to the original 

 article by Goodner and Horsfall. 



Bactericidal Tests (Ward 1480 ) 



In this method, a constant amount of whole blood is placed in a series 

 of tubes, and to each of the tubes is added a decreasing number of or- 

 ganisms, so that — for example — the first tube is inoculated with 500,- 

 000 organisms, the second tube with 50,000 organisms, the third tube 

 with 5,000 organisms, and so forth. The tubes are sealed and placed in 

 a rotating box in the incubator. After some hours' incubation, the tubes 

 are opened and the contents plated. The plates are incubated and read 

 the next day. It is evident that the sterility of the contents of the tubes 

 — as shown by the plates — depends on three main factors, namely, the 

 number and virulence of the organisms, and the phagocytic power of the 

 whole blood. As the number of organisms can easily be controlled, the 

 method can be used to determine either the virulence of the organisms, 

 by always using the same blood, or the phagocytic power of the blood, 

 by always using the same organisms, providing their virulence is main- 

 tained at a constant level. The maximal number of organisms killed in 

 the mixture is, in the one case, the direct measure of the phagocytic 

 power of the blood and, in the other case, the indirect measure of the 



