Five years now elapsed before Hahnemann published anything more in the line of drug pathogenesy. They must have been five years of intense labor and experiment. Then appeared the first volume of that great classical work, the "Materia Medica Pura," containing the symptomatology of twelve medicines, six of which had already appeared in the Latin treatise published before.

Five years later appeared the second volume, containing the symptomatology of eight medicines, which was soon succeeded by the four other volumes, containing in all the pathogenic effects of sixty-one drugs. It is a monumental work, the result of Hahnemann's matchless penetration, wonderful insight and accurate observation, of which he was a master. He was most ably assisted in this work by thirty-five fellow-provers, among whom the names of Franz, Gross, Hartmann, Herrmann, Hornburg, Ruckert, Stapf, and Friedrich Hahnemann are the most conspicuous and deserve to be remembered by all students of Materia Medica.

In 1822 appeared a second edition of this great work, with considerable additions to the symptomatology of all the remedies and some new medicines besides. A third and fourth edition were published after some years.