Intracerebral injection of vaccine into the mouse induced swelling of the brain. The swelling reached the maximum in the intensity by day 1 and persisted for several days. A method for quantitative determination of the brain-swelling activity of the vaccine was developed. A positive regression coefficient was found only between the brain-swelling and the lymphocytosis-promoting activities. Such activity was no longer shown with the vaccine heat-treated for 30 min at 80 C, but it was restored upon addition of the lymphocytosis-promoting factor (LPF) that caused no brain swelling by itself. The activity, therefore, was ascribed to cooperation of LPF and a certain heat-stable component other than endotoxin contained by pertussis vaccine.

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The pathologic manifestations of the toxic death elicited by the iv injection of mice withRiekettsia tsutsugamushistrain Gilliam were examined by light and scanning electron microscopic techniques to ascertain the cause of death. Light microscopic examinations of hematoxylin and eosin-stained sections of organs suggested the presence of fluid in the lungs; this was confirmed by an increase in the weight of the lungs of moribund mice. Scanning electron microscopy of blood cells demonstrated a marked crenation of erythrocytes from these mice. Death appears to be the result of shock brought on by vascular collapse secondary to plasma leakage.

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The antigenic scheme forPlesiomonas shigelloidesdescribed by Shimada and Sakazaki (1978) has been expanded to 107 serovars consisting of 50 O serogroups and 17 H antigens.

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