The knowledge that investigators are gaining in the laboratory and are trying to give to the community must be accepted and applied by the individual. How is the individual, discouraged by sickness and hardship, to know that things are awry or that they can be set more nearly straight? How can he know that he is responsible for his limitations? Why should he suppose that he need not be eternally a slave to environment? How can he realize that “health promotes efficiency by producing more energy and leaving it all free for useful purposes?” A few enlightened souls recognize the tendency of environment to kick the man that is down; to be subservient to the man of bodily and mental vigor, of keen understanding and human insight, but the majority must be led to believe these scientific principles. Again and again scientists and humanitarians must return to the attack, for individual carelessness becomes community menace, and “line upon line and precept upon precept” they must present their knowledge in language that shall attract and hold the attention and fancy. So the work and discoveries of Metchnikoff have gained credence because the disciple who described them had the ability to impress on his audience in a convincing fashion the one fact that made a strong appeal--the possibility of long life. If those who are zealous for any movement would study the psychology of advertising and speak as forcefully as the legitimate advertiser, they would be more persuasive and successful. When an idea has won in a certain circle, it quickly spreads to the other members, thence to active communities. So the universal law of imitation may be the greatest help in the spread of ideas. The individual eats a certain food because his neighbor does. Boston determines to make an effort for a better city because Chicago has felt the stirrings of civic pride. A gifted individual with a deep sense of the need of his community sees an ideal condition, which by his thought becomes a possibility. These beliefs he shares with a few choice spirits till the circle has widened. The new ideas come to the notice of the city or the town officials, new means are adopted of educating the whole community, and, if necessary, legal measures are passed. But the new means to betterment must be applied by the individual. Beginning with the exceptional individual and ending with the average individual, the perfect circle is rounded out.