The Reactions of Rat and Mouse Eggs to Hydrogen Ions

Abstract

The mammalian egg is enclosed by a transparent membrane, the oölemma or zona pellucida, which disappears as the blastocyst implants itself in the uterine wall. Various suggestions, unsupported by experimental evidence, have been advanced as to the factors concerned in the removal of the egg membrane within the uterus. In the course of studies in vitro on rat and mouse eggs, it was found that eggs placed in acidified Ringer's solution rapidly lost the zona. No difference was observed between the reactions of rat and mouse eggs but occasionally eggs from the same animal showed marked differences. In one case, the zona of a 4–celled rat egg swelled and disappeared in 10 minutes, while the zona of a second egg (8–celled) remained unaffected after several hours in the same drop of fluid (pH 4.3). Practical use of this method of removing the zonae has been made in the study of the development of the isolated blastomeres of the rat. 1

Rat and mouse eggs, from the 2-celled to early blastocyst stages, were cultured at room temperature by the hanging drop method in depression slides. For aid in these experiments, I am greatly indebted to Dr. J. S. Nicholas, who removed the uterine tubes from the animals and obtained most of the eggs. The eggs were obtained by mincing the uterine tubes in unbuffered Ringer's fluid in an embryological watch glass, and after a few minutes removing the eggs with a capillary pipette under a binocular dissecting microscope. The eggs were transferred to a second watch glass filled with unbuffered Ringer's fluid and then to the test solutions.