Young adult and adult rats whose cerebellum was focally irradiated with a variable number of daily doses of 200 r X-ray during infancy were tested for spontaneous locomotion, in activity wheels, for muscular strength, in a weight-pulling apparatus, and, for skill in coordination, in a rope-climbing apparatus. Spontaneous activity declined as a function of number of daily irradiations; the interaction of treatment, age, and prior experience was also investigated. Weight pulling capacity, as determined by running time in an alleyway, was not affected by irradiation with 1 to 4 X 200 r with loads equalling the rats' own body weights. Ease of rope climbing was inversely related to the number of daily irradiations in terms of climbing time, number of shocks received, falls off the rope, and other criteria. cerebellum X-irradiation locomotion muscular strength activity wheel N THE first paper of this series (Wallace and Altman,
I this issue) we reported on a number of qualitatively assessed motor deficits in infant adolescent rats whose cerebellum was irradiated after birth with repeated daily doses of 200 r X-ray. Correlated with retarda- tion of cerebellar development, which was a function of the number of doses delivered on successive days, we observed several locomotor deficits. Among these were reduction in "general activity," tremor, and ataxia. Most of these symptoms were appreciably attenuated or disappeared by the 30th day, except in the animals that received 8 to 10 x 200 r. T h e experiments described in this paper were carried out on youngadult and adult rats. These tests were undertaken on the assumption that even in rats with fewer doses of X-ray, abnormalities in locomotion might be detected