Abstract
1) Temperature was recorded continuously at various depths in the brain tissue of unanesthetized but moderately restrained chickens. The chickens were kept in a small round arena within a soundproof chamber and exposed to constant illumination for up to 18 days. Activity on a spring-suspended floor in the arena was recorded on print-out counters. Light intensity was varied from 0.05 to 100 lux, but was kept constant for at least 24 hr and in most experiments for several days.
2) The brain temperature and most of the activity of all chickens showed clear circadian rhythms. For each condition, the following parameters were computed: mean level of brain temperature, range of circadian oscillation, and amount of activity.
3) Level of brain temperature and amount of activity were positively correlated with light intensity. For the range of brain temperature oscillation, such a correlation was indicated by one statistical test, but the correlation was not significant with increased intensity in two other tests.
4) Range of oscillation seemed to be positively correlated with brain temperature levels at lower values, and negatively correlated at higher values of mean level.
5) The changes in brain temperature in response to changes in light intensity were rather abrupt and simultaneous in all parts of the tissue.
