The work of a homeopathic student while studying and applying materia medica is to constantly compare and differentiate. He must compare the pathogenesis of a remedy with the recorded anamnesis of the patient; he mustdifferentiate the apparently similar symptoms of two more medicinal agents in order to select the simillium. To enable s student or practitioner to do this correctly the student must have proper knowledge of the individuality of the remedy; something that is peculiar, uncommon, or sufficiently characterstic in the polychrest remedy that may be used pivotal point of comparison. This pivotal point may be 'keynote' a 'charcterstic' or the 'red strand of the rope'. This excellent work by Dr H C Allen helps the reader to grasp the PQRS symptoms in no time.