Chemical toxicity testing. Scientist testing the effect of chemicals on the chorioallantoic membrane (CAM) of a chicken embryo. The CAM is a vascular membrane found in eggs of some amniotes, such as birds and reptiles. This test, known as a HET-CAM (hen's egg test-CAM) test, is designed to help assess the likely biological response of a human eye to certain chemicals. Photographed at the International Centre for Toxicology (CIT), Evreux, France.