“…Firstly, the lymphocyte donors have had tumours quite differently sited and histologically different from those serving as sources of antigen; secondly, the effect of the common tumour antigen (indirectly) on the macrophages seems to be maximal (Carnegie et al, 1973) and response to further antigens would produce no extra slowing. The results obtained by Bjorklund over several years (see inter alia Bjorklund and Bjorklund, 1957;Bjorklund, 1961Bjorklund, , 1968 which have very recently come to our notice, suggest that other methods of detection of a common antigen are practicable, though failure to detect such an antigen has led to the current belief that it cannot exist.…”