Although tumours were perhaps his greatest interest, Virchow never completed this work which was intended to have 30 lectures. Instead he stopped with the 25th lecture, on carcinoma, probably because of the vigorous attack which Remak and others were making on his conception of the histogenesis of epithelioma. Virchow’s 25th lecture records one of his mistakes – his theory of the connective-tissue origin of carcinoma. So great was Virchow’s influence that this error was not generally recognized until the work of Waldeyer (see No. 2620).