When the eye of man first contemplated the hitherto invisible world of minute plants, a most bewildering vegetation presented itself: plants without chlorophyl that decompose dead organic matter, and form an important link in the chain of life itself; plants that prey on vegetation that embellishes homes and furnishes food; plants that have finally left their natural habitat and seek their sustenance directly by parasiting man. Into this garden of flowers stepped the great master, Pasteur. Lingering but a short while in contemplation of the relatively large fungi, the yeasts, he quickly scented the haunts of man's greatest enemies, the tiny bacteria. And from that day to this, men have been treading the paths that run here and there through this apparently limitless labyrinth of strange vegetation to search out and to destroy these, the least in size and development, yet the greatest in power for evil. It is only