1. purpose of the Experiment.The present experiments were designed to study the conditioned behavior of a white rat in the Skinner-Perin box. Especially, the reaction latencies in the process of conditioning were chief concern. And it was done to realize the moment of systematization of random bebaviors in the reaction latencies.2. Experimental Procedure.A. Subjects.The subjects for the present experiments were 38 white rats. The ages of the animals ranged from 100 to 130 days in the first day of experiments. And their weights were about 100grs. for each.B. Apparatus.The apparatus shown in Fig. 1 is Skinner-Perin box. The brass bar which the animal had to learn to press projected into the compartment through the slot in the brass pannel. If the responses made, the circuit of release mechanism was closed and reinforce ments were given. A vertically sliding sheet-metal shutter in front of the brass bar was operated by the experimenter. It was lifted by the pulling of thread from outside the box when the animal had taken its place before if in readiness, and lowered when the animal gained the food cylinder from the food tray.C. Procedure.The animals were divided into three groups: the first (time group A), the second (time group B), and the third (frequency group).The first group was subdivided into three groups: 10 minutes group (2 animals), 30 minutes group (3 animals), they were trained freely in a given time per day. The second group was the same as 30 minutes group of the first (12 animals). The third group, however, was not restricted by time but frequency of responses, and was given 100 reinforcements, five responses per day (18 animals).The reaction latencies, that is, the time from the lifting of the shutter to the animel's reaction, were recorded.3. Results.A. The first group.The frequency of responses increased as the number of the days of reinforcement increased, and contrarily it decreased as the number of the days of experiment increased. But 10 minutes group was failed to establish of conditioned behavior.The percentage distribution of reaction latencies longer than 20sec. was very zigag and irregular. It was found, however, that the percentage distribution of reaction latencies shorter than 20sec. resembled to the ditribution of response frequency, and was considerably regular. We think from these results that the moment of transformation from random to systematic behaviors lies in up to 20sec. from the view point of reaction latency.B. The second group.By the method of statistical paired comparison, we, from this experimental data, attained the determinati on of SER, SLR, and so on that Hull used in his Principles of Behavior as the intervening variabls.And thus we could find the probabilities of (SER-SLR) values when they exceeded zero value corresponding to the number of reinforcements. It was considered from the statistical point of view that the fifty percent probability of them was the moment of systematization of behavior, and it corresponded to the reaction latency, 11.6sec.C. The Third Croup.By the same method as the second experiment. we could determine the moment of systematization among the given reaction latencies: 11.8sec.