The leptospiral agglutination test of the blood of 133 presons, of whom 126 were suffering from uveitis and 7 healthy, in the Chugoku District of Japan between 1954 and 1956, revealed positive results in 48 cases. The positive cases were of the following types: L. icterohemorrhagiae14; L. hebdomadis30; L. australis A4; L. canicola6; among these are included 4 mixed infection of L. icterohemorrhagiae and L. hebdomadis and 2 mixedinfection cases of L. hebdomadis and australis A. Two dogs belonging to the patients of Canicola fever had positive agglutination titers for L. canicola and one strain of L. canicola was isolatedfrom one dog.

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In recent years, the relationship between exogenous bacteria and normal intestinal flora has been investigated by various workers in studies on the developmentalmechanism of intestinalinfectious diseases. As a method of studyinge this subject, particular organisms were purposely administered perorally and from their multiplication in the intestine the above mentioned relationship was analogically constructed. In this type of experiment, however, there was a disadvantag that by keeping certain numbers of experimental animals in a cagecross-infections could take place among them and even by keeping an animal separately in each cage a similar possibility had to be expected when animals which have the habit of coprophagia were employed.
It was previouslyfound by the present author that when Ballerup and Shigella flexneri 2b resistant to 1, 000μg/ml of streptomycin were suspended in 1, 000μg/ml solution of streptomycin, and each organism was perorally administered to mice for 3 days successively Shigella organism multiplied in their intestinal tract twice aslong as when it was given alone with the same method. In this experiment, however, the possibility of theabove mentioned cross-infection could not be excluded, and it was decided to study this problem in the present paper.
In the present studies, Ballerup strain No.20 (Kitasato Institute) which was made resistant to 1, 000μg/ml of streptomycin was perorally administered in varying doses using a special syringe. Each mouse was separately kept in each cage and prior to theinfection, 0.2 ml of 10μg/ml solution of streptomycin was perorally given once daily for 3 days. Thefeces were cultured on BTB-lactose agar andBTB-lactosestreptomycin agar.
In studying the conditions for causing cross-infection, the following facts were found. When the purposely made carrier mice were kept together with normal mice, cross-infection occurred only when more than 10⁶ cells of Ballerup were excreted in each piece of stool. But, unless the normal mice were pretreated with streptomycin, they did not become infected.
From these findings, it is assumed that cross-infection is able to take place only shortly after the peroral administration of the organism under the conditions of the previous study, and it is apparent that the possibility of cross-infection does not affect the previous conclusions on the coexistential multiplication of Ballerup and Shigella flexneri 2b in the intestinal tract of mice.

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