[Abnormality in the behaviour of mice after an experimental encephalitis by yellow fever virus 17 D. Experiment model(author's transl)].

Viral encephalitides in infants are very often followed by serious mental manifestations. To be able experimentally to investigate this pathological phenomenon, we established the following model. Mice having recovered from an intracerebral infection with yellow fever virus 17 D (routine test for the potency of yellow fever vaccine) and giving the impression of normal and healthy animals were examined for their psychical behaviour. As unit of measurement we took the time for running through a labyrith (fig. 1). At the entrance of the labyrith in a box there was placed the population of animals of one cage (6 animals in maximum) and at the opposite side there was deposited the food. The animals going to be examined had been without food for 24 hours. The time was taken having passed from the moment of placing the animals up to the moment of their nibbing at the food. We examined 11 groups of mice having past routine tests for the potency of the yellow fever vaccine. One of them had been tested twice at an interval of 54 days (table 1). The 791 mice which had passed the encephalitic infection showed an average running time of 8.90 min. The 164 controls, however, had an average running time of 4.37 min (table 2). This difference is significant (p=greater than 1/1000). The average running time is proportional to the injected virus quantity (table 3). The significance of each single virus dilution to the group of normal animals is always greater than 1/1000. The significance is more than 1/100 for each single virus dilution between 10(-1) and 10(-3) compared with the virus dilution of 10(-5). Immediately after the clinical period (21 days), no difference could be observed between the single virus dilutions. After 76 days only, the test showed the above mentioned differences (table 4). Therefore, the mice having found their food after a long running time had more serious postencephalitic lesions than those having had a shorter running time. To prove this statement, we examined histologically brains of 14 mice which had found their food after 20 min on an average and those of 16 mice having had an average running time of 6.58 min. The histological evaluation was performed in regard to eight pathological characteristica. The results were recorded on tables for each slide with a histological preparation. For this we used squared paper (fig. 2, 3). For each brain of mice, the so-called "index of lesions" was calculated by the proportion of labelled and all squares. .....