THE UNITY OF HISTORY. 249 of assimilation, under our political and social system, has been equal to every demand upon it. We need to know not merely what the general and essential qualities of civilization and of our social nature really are ; but we require to know the general course in which they are tending. The more closely we look at it, the more distinctly we see that progress moves in a clear and definite path, under the principles and control of primordial law. The development of man in history is not a casual or arbitrary motion ; it moves in a regular and consistent plan. Each part is unfolded in due order the whole expanding like a single plant. More and more we see each age working out the gifts of the last, and transmitting its labors to the next. More and more certain is our sense of being strong only as we wisely use the materials and follow in the tracks provided by the efforts of mankind. Everything proves how completely that influence surrounds us. The earth's surface has been made, as we know it, mainly by man. Study of the earth, as modified by human agency, is one of the most interesting and profitable themes of history. The earth would be uninhabitable but for the long labors of those who cleared its primeval forests, drained its swamps, first tilled its rank soil. Man must overcome nature. The Mississippi Valley would be practically unhabitable had not the use of quinine taught man how to overcome ma- larial fevers, of which now he has but just begun to ascer- tain the true cause. Let us not forget that all the in- ventions upon which we depend for our existence, all the instruments we use, were slowly worked out by the neces- sities of man in the childhood of the race. We can only modify or add to these. We could not discard all existing machines and construct an entirely new set of industrial implements. To break with our past, were it possible, would be to reduce us to the conditions of primitive life.
