It is human experience that as a man concentrates his efforts, either mental or manual, his skill in his chosen specialty, and the quantity of his product increase. It was shown... that specialization in machinery had a powerful influence in specializing the workman and thereby extending the principle of division of labor. But division of labor may be furthered by other influences. The very growth of all lines of human knowledge and activity makes it increasingly difficult for one man to retain a grasp of any one entire field. He must be content to cultivate a small portion of it.

p. 47 - Principles of industrial organization, 1913