Studies on the Growth of Tissues In Vitro

Abstract

1. Embryo juice initiates in cells growing in plasma alone a process which after a latent period of some 10-12 hours culminates in cell division, and it is not necessary for the embryo juice to be present in any appreciable amount during the actual division process. 2. The approximate minimum effective dose is 5 per cent embryo juice in Tyrode solution acting for 3 hours. 15 and 40 per cent juice produce marked effects when applied for only 1 hour. 3. The concentration of embryo juice is a more important factor in determining the number of mitoses produced than is the time for which it acts. 4. Unless the embryo juice remain in contact with the culture for more than 10 hours, only one crop of mitoses occurs; but if it is present in the medium during or after the occurrence of the first divisions, then a second crop of divisions takes place. Evidence is adduced that it is the daughter cells produced during the first crop of mitoses which divide to produce the second crop. 5. The duration of mitosis is correlated with the concentration of the embryo juice. It approaches a minimum of about 40 min. 6. The duration of mitosis, particularly that of the ana- and telophases, is correlated with the rate of migration of the cells. 7. When a second crop of mitoses occurs in these cultures which have passed through a period in plasma alone, there is evidence that the size of the cells in metaphase of mitosis is significantly less than that of the cells of the first crop.