Precision delivery of small volumes of liquids to very young avian embryos: II. Description of the injection system

An instrument is described and its use detailed for injecting small volumes of liquids into the yolk of very young chicken eggs so that they have a high probability of contacting the embryo within a short period of time. The egg is positioned on its side with the candled embryo oriented precisely uppermost. A tiny hole is drilled through the shell, but not the shell membranes, on the bottommost surface of the egg. Then a 2-in. (51-mm), 23-gauge hypodermic needle is inserted vertically through the hole to a point where its tip lies 5 to 8 mm below the embryo (8 to 10 mm from the cross hairs in the Lucite tube support). The desired volume of fluid (25 to 100 μl) is then delivered by a remote precision microsyringe joined to the needle by fine bore flexible tubing. The needle is then withdrawn and the shell hole sealed with melted paraffin. After the injection, the egg is returned to the incubator with the candled embryo uppermost.