Excerpt from The Journal of Comparative Psychology, Vol. 1: Robert M. Yerkes The method of investigation of learning and the number of trials given were the same as those adopted with the two previous problems. One trial a day method was used. All rats were 40 days old when fed for the first time on the upper platform. T hey were fed 3 at a time for a period of 20 minutes for two successive days. Approximately 50 rats were used. Oi these, 20 were used for the preliminary investigation of the problem. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.