The chick embryo in toxicology: an alternative to the rabbit eye.

The chorioallantoic membrane (CAM) of the chick embryo is readily accessible for experimentation. It is a complete tissue that responds to injury with classical inflammatory reactions. It is limited to the late phase of embryologic life, and is without the sense of pain. Focal topical application of various household products onto the CAM results in local injury and reactions that differ in severity from one product to another. For any single product, tested as a sequence of dilutions on a series of membranes, the CAM responds with decreasing intensity that parallels the decreasing dosage. The membrane is prepared for study according to the method of Zwilling (Transplantn Bull 1959, 6, 115). The test material is applied in a Teflon ring to the 14-day-old CAM, to localize the application site. The macroscopic response is scored on day 17 of incubation. The results of analysis of histological preparations are found to correlate with macroscopic appearance. When a series of preparations was ranked according to the severity of the response each induced on the CAM, there was a good correlation with the ranking of the same preparations in the Draize test.