If fertilized fish ova are placed in a 50 percent solution of wine vinegar [any ordinary vinegar will probably be found to answer just as well] the embryo, even during the very first stages of development, will become apparent to the eye lying on the transparent yelk. The acetic acid contained in the mixture, one part water to one part wine vinegar, causes the material of the embryo proper to coagulate, while the yelk remains clear.
A short time after the ova are laid in this mixture, and during the first week after impregnation, a white circle at one pole of the egg should become apparent, and in the course of the second week a cylindrical white streak running from the edge of the circle toward its center should be evident. If these features are not developed by the test, the eggs have not been fertilized, and are, therefore, worthless.

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