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From 17 patients with different forms of acute leukaemia, mononuclear blood cells were cultured in diffusion chambers (DC) implanted intraperitoneally into pre-irradiated mice. In 14 patients, growth of blast cells could be observed during the culture period of up to 21 days. To question whether this growth of blast cells was due only to proliferation of the initially proliferating fraction or whether a re-entry of resting leukaemic cells into proliferation was involved, various 3H-thymidine (3H-TdR) labelling studies were carried out. The absolute increase of blast cells in EC showed no correlation with the fraction of leukaemic blast cells in DNA-synthesis in the implanted cell suspension as measured by 3H-TdR labelling in vitro. Furthermore, in 2 patients where the kinetic behaviour of initially labelled leukaemic blast cells was followed during DC culture, the increase in total blast cells could only be attributed to a small extent to proliferation of those cells initially in the cell cycle. Lastly, "in vivo" labelling during the culture period showed that in one case 25% and in another case 60% of the blast cells in DC were proliferating. The conclusion is that, owing to the stimulation of the diffusion chamber milieu and possibly also due to removal of an in vivo inhibition, in most cases of acute leukaemia resting leukaemic blast cells can apparently re-enter the active cell cycle. This has relevance for an understanding of the self-maintenance of the leukaemic cell population and may also be a reason for relapse of leukaemia after the usual cytostatic drug treatment which affects mainly the proliferating leukaemic cells.

Das hydrodynamische und thermische Verhalten einer Flussigmetallstromung wurde bei benetzter und nichtbenetzter Rohrwand untersucht. Als Modellfluid diente Quecksilber. Bei laminarer Stromung wurden keine hydraulischen Anomalien nachgewiesen. Beim benetzten Rohr wurde eine standige Durchmesserveranderung und Erhohung der Rauhigkeit beobachtet, die auf die Bildung und Abtragung einer Amalgamschicht an der Wand zuruckzufuhren ist.

Growth of mononuclear cells from human peripheral blood from 10 normal individuals was tested in diffusion chamber culture over a period up to 17 or 21 days. After an initial decrease during the first few days an increase of the total cell number was observed with maximal values on day 13. In all individuals growth of undifferentiated blast cells, lymphocytes, plasma cells, immature and mature granulopoietic cells, macrophages, and megakaryocytes occurred. In all individuals the different cell types had similar growth patterns in diffusion chamber culture. The considerable numerical variations which were seen in the granulopoietic cells were probably due to different stem cell concentrations in the peripheral blood of the investigated individuals. The results indicate that the diffusion chamber technique is a valuable method for the detection of haemopoietic stem cells and the culture of lymphocytic cells in man.