Abstract
It has recently been shown possible to consider the precipitin reaction as a series of competing bimolecular reactions 1 and so derive from the mass-law an expression
in which R is the ratio of antibody to hapten or antigen in the precipitate at a reference-point in the equivalence-zone, and A is the amount of antibody-N precipitated at the reference-point. This equation describes closely the behavior of a number of immune precipitating systems.
Since the agglutination reaction may be considered a precipitin reaction at the bacterial surface, it was thought that the above theory might be applied. The test involved the development of an absolute method for the micro-estimation of agglutinin 2 and the use of a single hapten at the bacterial surface and the homologous antihapten. This was realized in a freshly washed, heat-killed pneumococcus IS (Dawson “M”) suspension and, for the antibody, Type I antipneumococcus horse-serum freed from antibodies other than type-specific anti-carbohydrate by absorption with “C” substance and pneumoeoccus IR (Dawson “S”) suspension. 3 Typical runs are given in Table I and show excellent agreement with the calculated curves and values. Agglutination differs from precipitation in that a maximal N:S ratio is obtained at a relatively small excess of antibody.
It would appear, therefore, that a quantitative chemical theory has been found capable of accurately describing a typical instance of bacterial agglutination. This theory makes no distinction between the initial chemical combination of multivalent antigen (or hapten) with multivalent antibody and the subsequent flocculation. 4 That this so-called second phase of agglutination is also due to the building up of large aggregates by chemical combination of antibody on the bacterial surface with antigen (or hapten) on the surface of other bacteria is indicated by the following:
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