The formation and destruction of long chains by growth of Group A streptococci in the presence of type-specific antibody have been studied with the fluorescent antibody technique. Long chain formation has been shown to depend on the presence of free antibody during the growth of the bacteria. Destruction of long chains has been shown to depend on the continued growth and division of the bacteria in the absence of free antibody.

Univalent antibody fragments formed by proteolytic digestion of antibody globulin have been shown to have the combining properties of untreated antibody but do not result in the production of long chains.

A model involving end-to-end agglutination during growth of Group A streptococci has been presented to explain the mechanism of production of long chains by growth of Group A streptococci in the presence of type-specific antibody.

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