"Young men," said a wise physician in addressing a class of graduates in medicine, "you are about to enter the battle of life. Note that I say the 'battle' of life. Not a playground, but a battlefield is before you. It is a hard contest--a battle royal. Make no mistake as to that. Your studies here have furnished your equipment; now you must go forth each to fight for himself." The same words might be said to every neophyte in whatever walk of life. The pursuit of every trade, every profession is a battle--a struggle for existence and for supremacy. Partly it is a battle against fellow men; partly against the contending powers of Nature. The physician meets rivalry from his brothers; but his chief battle is with disease. In the creative and manufacturing fields which will chiefly concern us in the following volumes, it is the powers of Nature that furnish an ever-present antagonism. No stone can be lifted above another, to make the crudest wall or dwelling, but Nature--represented by her power of gravitation--strives at once to pull it down again. No structure is completed before the elements are at work defacing it, preparing its slow but certain ruin. Summer heat and winter cold expand and contract materials of every kind; rain and wind wear and warp and twist; the oxygen of the air gnaws into stone and iron alike;--in a word, all the elements are at work undoing what man has accomplished. THE STRUGGLE FOR EXISTENCE In the field of the agriculturist it is the same story. The earth which brings forth its crop of unwholesome weeds so bountifully, resists man's approaches when he strives to bring it under cultivation. Only by the most careful attention can useful grains be made to grow where the wildlings swarmed in profusion. Not only do wind and rain, blighting heat and withering cold menace the crops; but weeds invade the fields, the germs of fungoid pests lurk everywhere; and myriad insects attack orchard and meadow and grain field in devastating legions. Similarly the beasts which were so rugged and resistant while in the wild state, become tender and susceptible to disease when made useful by domestication. Aforetime they roamed at large, braving every temperature and thriving in all weathers. But now they must be housed and cared for so tenderly that they become, as Thoreau said, the keepers of men, rather than kept by men, so much more independent are they than their alleged owners. Tender of constitution, domesticated beasts must be housed, to protect them from the blasts in which of yore their forebears revelled; and man must slave day in and day out to prepare food to meet the requirements of their pampered appetites. He must struggle, too, to protect them from disease, and must care for them in time of illness as sedulously as he cares for his own kith and kin. Truly the ox is keeper of the man, and the seeming conquest that man has wrought has cost him dear.