Measurement of mechanical forces acting on the area pellucida of the early chick embryo.

We have designed a method for measuring mechanical forces acting on the area pellucida of the chick embryo between stages 1 to 5 of HAMBURGER and HAMILTON (1951). The coordinates of several points on the outline of the area pellucida were used as input, from which a computer program measured the changes in the position of similar points to produce a table of values which, we argue, reflect mechanical forces in the embryo. The results obtained are shown to be reproducible between embryos. The computer program and the measurements obtained were then used to predict the behaviour of surgical incisions made in the area pellucida, using the tables obtained from direct measurements of embryos and the coordinates of various points on the surface of the operated embryos. This procedure was applied to embryos cultured by the method of NEW (1955) and in-ovo. It was found that in those embryos cultured by EWS technique the computer predictions correspond very closely to shape measurements made directly from embryos. However, the correspondence is less close when applied to embryos in-ovo.