Printed in Great Britain © Company of Biologists Limited igyS THE EFFECTS OF TUMOUR CELLS ON EMBRYONIC CELL AGGREGATION, ADHESION AND DETACHMENT

The presence of small numbers of tumour cells inhibits the aggregation of embryonic chicken neural retina cells grown in gyratory shaker culture. The aggregation of neural retina cells was also inhibited by ascites cell medium. We investigated whether the inhibitory effect of the tumour cells on aggregate size is effected by inhibition of the initial adhesion or by enhance-ment of their separation. The number of neural retina cells adherent to microtest plate surfaces was significantly reduced after incubation with either Ehrlich ascites cells or cell-free, condi-tioned medium, while the percentage of cells removed from glass by shearing was unchanged under those conditions. These results suggest that the reduction in neural retina cell aggregate size produced by Ehrlich ascites cells and their products is due to partial inhibition of neural retina cell adhesion processes, as distinct from enhancement of separation