Intranuclear inclusions were found in 75 per cent of young mice suffering from a spontaneous diarrheal disease. They were confined to the epithelial cells of the small intestine, and to the intestinal and mesenteric lymphadenoid tissue. They were seen only between the 10th and 15th days after birth, in apparently healthy control mice of the same age group, they were found in only two of thirty-six animals (5.5 per cent) and these were in mice from the same room and stock as the diseased animals.

Nursing mice experimentally infected by feeding unfiltered diarrheal feces, also showed inclusion bodies from the 10th to the 14th day inclusive. The inclusions were not present during a corresponding age period, in the healthy stock used for these experiments.

Inclusions have also been found in the cytoplasm of the intestinal epithelial cells of young mice but without any significant relation to the disease under study. No conclusions as to their nature are warranted at this time.