Guinea-pigs infected with Group C streptococci develop an altered response to subsequent injections of homologous strains. This behavior may be manifest as early as five days following primary infection. Lesions developing upon reinfection by the intracutaneous route differ from primary cutaneous lesions in that they develop and regress at an accelerated rate. Reinfection lesions are usually healed within one week after being induced, while primary cutaneous lesions are more persistent and do not heal before the twelfth or fourteenth day.

The experiments indicate a difference in the degree of immunity enjoyed by guinea-pigs exhibiting the altered response produced by infection. Those which were infected for only six days before the reinfecting dose was given, developed severe allergic response at the point of inoculation, and later lesions of regional lymph nodes. Animals infected for three weeks or more before reinfection was attempted developed accelerated local cutaneous reactions, but did not develop lesions of regional lymph nodes.

Slight cutaneous sensitiveness to streptococcal extracts was produced in guinea-pigs by repeated injections with killed streptococci, but the animals had little or no immunity, and behaved like normal controls when infection was induced by the intracutaneous routes.

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