It was a great pleasure and honour to have been invited to attend this Seminar and to present a final impression. The association in this field between the Chester Beatty Research Institute and Dr. Rosenberg's School at East Lansing is something which I specially value and many would doubtless like to know how it came about. In the course of its work in carcinogenesis and on chemotherapy over many years, the Chester Beatty Research Institute was frequently drawn to the importance of many metals - as for example lead, iron, metalloid arsenic and the metalloid quali- ties of the carcinogenic...