POSTSCRIPT OF 1919

less important in relation to feeling and activity than it is in related animals. This supremely important side of mental life, then, will be capable of continuous illustration and illumination by biological methods. It is on the intellectual side of mental life that man’s congruity with other animals is least obvious at first sight. The departure from type, however, is probably a matter of degree only, and not of quality. Put in the most general terms, the work of the intellect is to cause delay between stimulus and response, and under circumstances to modify the direction of the latter. We may suppose all stimulation to necessitate response, and that such response must ultimately occur with undiminished total energy. The intellect, however, is capable of delaying such response, and within limits of directing its path so that it may superficially show no relation to the stimulus of which it is the discharge. If we extend {244} the word stimulation to include the impulses arising from instinct, and grant that the delaying and deflecting influence of the intellect may be indefinitely enlarged, we have an animal in which instinct is as vigorous as in any of its primitive ancestors, but which is superficially scarcely an instinctive animal at all. Such is the case of man.