Abstract
The mitotic activity of lung colonies in the process of differentiation from mouse teratocarcinoma [OTT6050] cells injected in vivo was studied. The following 3 stages were identifiable with respect to the mitotic activity: a lag stage for a few days after injection; a stage during which maximum mitotic activity is observed for several days following the 1st stage; and a 3rd stage displaying a decrease in mitotic activity. There is a correspondence between the 3 steps in mitotic activity and differentiation in lung colonies previously identified by histological observations.