Langenbeck is reported by Paget1 to have said, What is it that decides what organs shall suffer in a case of disseminated cancer.... When a plant goes to seed its seeds are carried in all directions but they can only live and grow if they fall on congenial soil. This concept of the relation between the circulating tumor cell and the organ in which it becomes arrested has persisted to the present day. It is of practical importance to know more about this relation and the local factors which may influence it. While Engell,2 Cole et al.,3 and others have demonstrated the presence of circulating tumor cells, and Wood4 and Zeidman5 have investigated the in vivo micropathology of the arrested tumor cell, there is little known about the local factors which determine whether a cell at one site will become a metastasis, while at another