Nine strains of measles virus of different origins and passage histories were examined for their neuropathic properties in newborn hamsters and mice. The TYCSA strain, a clone variant of Toyoshima strain, was the highest in neurovirulence, and unattenuated Edmonston strain was found also to be highly neurovirulent. Unattenuated Tanabe strain and two wild strains failed to produce the illness in either animal species. Among the four attenuated vaccine strains, Tanabe-CAM and Schwarz strains were relatively of high neurovirulence on primary inoculation, but Leningrad-16 and Sugiyama strains were very low in virulence. With one of the low virulent strains, Leningrad-16, a limited growth occurred in the brain tissues of newborn hamsters after intracerebral inoculation, but no antibody response was detected in the survived animals. Increased resistance to the infection with the neurovirulent TYCSA strain was observed in the suckling hamsters of 7 or more days of age. Treating with anti-measles serum before infection was found to protect the newborn hamsters from the lethal effect of the neurovirulent strain.
As a model of human measles encephalitis, pathogenicity of the neurovirulent strain in producing encephalitis in newborn hamsters was discussed.

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Characteristics of the daily behavior and activity patterns of the adult housefly were investigated with special reference to time-keeping device. (1) Two of three strains and four of eight colonies of flies showed similar resting behavior patterns to those of the standard Takatsuki colony, whereas two colonies exhibited markedly different patterns. The remaining one strain and two colonies of flies displayed intermediate resting behavior patterns. Flight activity patterns exhibited by all strains and colonies of flies were essentially similar to those of the Takatsuki colony. The general behavioral pattern exhibited by male adults in groups was different from that of females due to the increased mating activity. Female flies exhibited decreased stability in settling on the ceiling of the container as they grew older, while the number of landing on the ceiling increased during the first few days of adult life and then stayed rather constant. (2) The flies were entrained to a 24-hr photoperiod with a 12-hr photophase. The circadian rhythm with 12-hr active phase persisted in individual flies for more than two weeks in continuous darkness, although in some cases changes in both the period of the rhythm and duration of the active phase occurred simultaneously. The flies in groups also continued to keep rhythmic behavior in continuous darkness at least for a week. Most individual rhythmic flies displayed only once the characteristic nighttime resting behavior at the expected onset of scotophase, while the individual flies held under continuous illumination from their emergence did not exhibit any sign of circadian rhythms. Individual flies kept in the actograph chamber also showed a rapid disappearance of the activity rhythm under continuous illumination. (3) In the flies subjected to a 24-hr photoperiod with a 14- to 20-hr photophase, the resting phase of the rhythm was moved ahead by about 1-4 hr. The time change correlated to the duration of the previous photophase. Majority of flies ignored the photoperiod with a 22-hr photophase. In the flies exposed to a 24-hr photoperiod with a photophase shorter than 6 hr, the resting phase was delayed by a few hours. This result accounted for the inexplicable resting behavior of flies in nature under long-day conditions. A single dark period of 6 hr or longer, interrupting continuous illumination, initiated the overt periodicity in the flies. The time of the onset of resting behavior was inversely related to the duration of a single dark period. (4) A single dark stimulus for the resetting was effective only when given after the critical time, viz, at 9 hr after the onset of illumination; whereas a cyclical change in the direct response to a single dark stimulus was manifested by the rhythmic flies, maximal response occurring at the onset of the resting phase and the minimal one immediately after the onset of light.

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