The analysis of motor conditioned reflexes was done on the base of Pavlovian strength law in experiments on monkeys and dogs. It was found that in normal experimental conditions direct strength relations significantly dominate. In extreme conditions which lower the excitability of the brain, direct strength relations sharply deepen, leading to narcotic phase. Comparison of the narcotic phase with other hypnotic phases brings to the understanding of the strength law within a wide range, from direct strength relations to reverse (paradoxical) ones, when narcotic and paradoxical phases are at different poles of the optimal state of the nervous excitability with their different mechanisms.