Modification of development in chick embryos induced by ultra-violet radiation.

Abstract

This is the sixth of a series of studies on radiation, four of which have concerned themselves with differential modification of embryonic development. The previous work includes experiments on Arbacia eggs and sperm, and on Fundulus eggs. The results in all the experiments agree in their more general features, namely, those regions which at the time of exposure have the highest rates of physiological activity, are the most readily modified in their development. Such modifications may be brought about by exposures made at various intervals after fertilization, as well as before fertilization. Experiments with hens' eggs yield the same general results, when exposed before and after incubation.

The complete spectrum of the Hg vapor arc (running at 110 v. D. C. at a distance of 10 inches) served as a source of radiation. Eggs were exposed at intervals, up to 64 hr. after incubation, as well as before incubation. Since it was found that exposures through the shell were entirely without effect, it was necessary to remove a small part of the shell and underlying membrane, and thus expose the blastoderm directly to radiation through the very thin layer of albumen which covered the surface of the yolk of the egg. Such a thin layer does not screen off the effective radiation. Exposures were from 1/5 min. to 10 min. in duration. It was found that later stages of development required less radiation to produce a given result, and would be killed with doses of 5 to 10 min. which produce only developmental modifications when exposures are made Before incubation.

Before incubation, or reincubation, the piece of shell which had been removed was replaced, and the egg sealed with paraffin. Development was usually allowed to continue for three days, although some eggs were removed from the incubator after 24 or 48 hours.