Science accumulates facts and principles which could never be determined by the common sense of the individual or community, and of so great a variety and generality that some of them are constantly passing over into practical life. The old farmer has learned the value of soil analysis, though with reluctance and suspicion, and he has learned to spray his orchards to preserve them from pests whose existence he did not suspect. At this moment science is advising him to put a bounty on the head of the turkey buzzard instead of imposing a fine for killing it. His common sense had told him that the vulture was valuable as a scavenger. Now science tells him that it is an ally of the paralysis fly and carries cattle, hog, and other diseases over the country. “Probably more than the income from a million dollars is spent each year in the several marine biological institutions for the study of three lowly forms,—the sea urchin and its progeny, the coral, and the jelly-fish.” An American entomologist has spent many years in measuring the influence of physical environment on potato bugs. He established colonies of these insects in Mexico, moved them from one temperature to another, one degree of humidity to another, one altitude to another, and recorded the changes shown in the offspring. He then moved the new generations back to the old environment and recorded the results,—whether the spots and other acquired characters changed or remained. His object was to determine certain laws of heredity,—whether and under what conditions new species are produced, whether acquired characters are hereditary. To common sense this procedure seems trivial, almost insane. But assuming that a biologist determines a law of heredity, this will presumably have a practical effect in the fields of agriculture, eugenics, crime, and medicine. These examples show that a science which results in a practical and efficient technic is constituted by treating it as an end in itself, not merely as a means to something else, and giving it time and opportunity to develop along all the lines of investigation possible, even if we do not know what will be the eventual applications of one or another of its results. We can then take every one of its results and try where and in what way they can be practically applied. We do not know what the future science will be before it is constituted, and what may be the applications of its discoveries before they are applied. But, on the other hand, the scientist will naturally be influenced in setting and solving his problems by the appreciation that if discoveries are made in certain fields practical applications will follow. He may know, for example, that if we can discover the scarlet fever germ we can control this disease, and he may work on this problem, or he may suspect that if we knew more of the chemistry of sugar we could control cancer, and may work on that problem.