Abstract
The learning rates of rats, as determined by means of a Skinner box apparatus, are compared for a control group and five test exposure groups. Exposure to an excess of negative ions yielded an increased learning rate, whereas excess positive ions impeded the learning rate. Exposure to carbon particles, alone and with excess positive or negative ions, resulted in improved learning rates over those from similar exposures in the absence of carbon particles. The synergistic effect of carbon particles is believed due to alteration of the ion balance in the atmosphere.