Prof. George Vithoulkas talks about the Phosphorus essense of materia medica during one of his homeopathic courses at Alonissos. Prosphorus is discussed and compared to other homeopathic remedies like Arsenicum, Nitric Acid, etc. You can find the complete teachings of Prof. Vithoulkas at the academic e-learning program http://www.vithoulkas.edu.gr