Studies on the Growth of Tissues in Vitro

In a previous number of this Journal (8) a method was described for measuring the growth rates of tissues in vitro. The colonies of fibroblasts were grown in modified Carrel flasks and photographed from below at regular intervals, so that a continuous record was obtained of the behaviour of the more peripheral cells of the colony over long periods of time. Mitoses could be easily observed, and the total number of cells on the field fairly accurately estimated. In this way the percentage of cells dividing per hour, or “mitotic index “, was calculated, and thereby a measure obtained of one of the more important factors concerned in the growth of tissues. By the use of this method it is possible to investigate the reaction of tissues to various growth-promoting or growth-inhibiting media, and to gain some insight into the general behaviour of growing tissues.