Amazing is it to see how near the world has come again and again to discovering the key to the cause and cure of pestilence.

It is now a matter of the simplest elementary knowledge that some of the worst epidemics are conveyed in water.

But this fact seems to have been discovered many times in human history.

In the Peloponnesian war the Athenians asserted that their enemies had poisoned their cisterns; in the Middle Ages the people generally declared that the Jews had poisoned their wells; and as late as the cholera of 1832 the Parisian mob insisted that the water-carriers who distributed water for drinking purposes from the Seine, polluted as it was by sewage, had poisoned it, and in some cases murdered them on this charge: so far did this feeling go that locked covers were sometimes placed upon the water-buckets.

Had not such men as Roger Bacon and his long line of successors been thwarted by theological authority,--had not such men as Thomas Aquinas, Vincent of Beauvais, and Albert the Great been drawn or driven from the paths of science into the dark, tortuous paths of theology, leading no whither,--the world to-day, at the end of the nineteenth century, would have arrived at the solution of great problems and the enjoyment of great results which will only be reached at the end of the twentieth century, and even in generations more remote.