Between various forms of communication the struggle for existence is as acute as it ever is between the wild animals and trees in the wilderness. When a message has once been delivered there is rarely any use in delivering it again. Whether the prime requisite be quickness, cheapness, accuracy, or any other quality, the form that serves the purpose best puts all the others out of business for that purpose, though of course the others may still be the best for other purposes. Wherever the railroad comes the stagecoach disappears; for some purposes the trolley has displaced the locomotive. A system of communication becomes better the larger it grows, other things being equal, and it has the advantage of what the economist calls the law of increasing returns. So the big railroads, telephone lines, newspapers, publishing houses, schools, absorb the little ones. Here and there, however, the small ones succeed because for some reason they are still the "fittest."