The development of the science of bacteriology has given rise to a new type of ’phobia—the dread of microbes. That vague dread of the mysterious and unseen or unknown which formerly attached to gnomes and kobolds now surrounds microzoa and bacteria, beings as invisible to the unaided eye of flesh and, to the popular fancy, ten times as full of maleficent power. The very word “microbe”—innocent enough in its definition of “a little living being”—has, in the minds of most persons, an ill-defined malign implication. Science itself has encouraged, though without design, this one-sided view of the activities of micro-organisms, for, naturally, the pathogenic germs have been studied before the non-pathogenic, and largely to the exclusion of the latter. Popular writing, moreover, usually exaggerates and often distorts the obvious trend of science.