Research Note: A Simple and Rapid Method for Dropping Chorioallantoic Membranes of Chick Embryos

Abstract

Usual methods of dropping chorioallantoic membranes (CAM) are time-consuming and some of them require experience and skill. A simple and effective method developed in this laboratory enables a single worker to drop the CAM's on hundreds of embryonated eggs per day. It has been used here successfully for neutralization tests of numerous serum samples with chickenembryo-adapted virus inoculated on dropped CAM. The only special instrument needed is an eggshell punch with a point almost exactly as long as the shell is thick. The punch is made from a dissection needle fitted with a rubber stopper such as used in vacutainer tubes. The needle is cut so that it only protrudes about 0.5 mm beyond the rim of the stopper. The rubber stopper acts as a bumper that prevents the shell from being cracked when punched, and the needle from being pushed too deep.. The procedure is as follows: a) The eggs are laid on their side, in rows on egg trays, with the airsac end :slightly upward. The upper surface is wiped with 3% iodine-alcohol solution. b) While the egg is observed with an egg candler, a hole is punched above the airsac and near its edge (Fig. 1:2). This can be done with any regular punch. c) With the sterilized special punch a hole is punched above the CAM (Fig. 1:1), approximately 1.5-3.0 cm from the hole above the airsac (Fig. 1:2). The punch is sterilized between eggs occasionally with 3% iodine-alcohol solution. d) With the egg still under observation, the CAM is dropped by suction with a rubber bulb on the airsac-hole (Fig. 1:2). The correct dropping is easy to control by observing the CAM-veins