Abstract
Discussion and conclusion
Although the circumoval reaction is species specific for S. japonicum, the results of the present studies show that with this test, there were cross reactions among the 4 geographic strains. A significantly larger proportion of eggs showing positive circumoval precipitation, however, was seen when the eggs were incubated with the antisera of the heterologous strains. This indicates that the geographic strains of S. japonicum have already become partly distinct in their serological characteristics.
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