The action of X-rays on the developing chick

This research was undertaken at the suggestion of Prof. Grünbaum, in order to discover whether any changes were produced in the chick embryo under the action of X-rays. Embryos of various ages were examined, both directly after exposure to doses of various amounts, and also at later periods. In none were any observations obtained of changes either in the embryo as a whole or in any particular organ, with the exception of one which affected all the tissues so exposed. It was found that X-rays had a general effect on the rate of division of the cells of the embryo, causing a diminution in the number of mitoses. This diminution was very evident in embryos exposed to long doses; for instance, chicks incubated for three days and then given a two hours’ exposure, showed so marked a diminution that a considerable search was required to find any mitotic figures, while in an embryo of three days, exposed for four hours, no mitotic figures could be found.