Guernsey made a name for himself in the 1870s as a professor of materia medica at Hahnemann Medical College in Philadelphia. He was a staunch supporter of Clemens von Bönninghausen. Under his influence, he developed his own "Keynote System." This efficient method has proven itself in countless cases since then. The result of Guernsey's studies is a highly condensed and reliable materia medica, reduced to the truly characteristic symptoms. For daily practice, this means an enormous guide for narrowing down the possible remedies.