Ch. 1— Summary, Policy Issues, and Options for Congressional Action • 9 
Figure 1-1.— Chronological Sequence of Chick 
Embryo Chorioallantoic Membrane Assay 
Day 17 
Day 0: Fertile eggs are incubated at 37°C. Day 3: The shell is 
penetrated in two places: A window is cut at the top, and 1.5 to 2 
milliliters of albumin is removed with a needle and discarded. The 
chorioallantoic membrane forms on the floor of the air space, on top 
of the embryo. The window is taped. Day 14: A test sample is placed 
on the embryonic membrane and contained within a plastic ring. Day 
17: The chorioallantoic membrane is evaluated for its response to the 
test substance, and the embryo is discarded. 
SOURCE: J. Leighton, J. Nassauer, and R. Tchao, "The Chick Embryo in Toxicol- 
ogy: An Alternative to the Rabbit Eye,” Food Chem. Toxicol. 23:293-298. 
Copyright 1985, Pergamon Press, Ltd. 
ism as a whole), testing may also be done to deter- 
mine the mechanisms by which a substance is 
metabolized or excreted, and the chemical re- 
actions by which toxic effects are produced. Such 
studies of mechanistic toxicology aid in the selec- 
tion and design of descriptive tests. 
The Federal Government plays a major role 
in this area, both through laws that directly or 
Chick Embryo Chorioallantoic Membrane Assay 
Photo credit: Joseph Leighton, Medical College of Pennsylvania 
Typical reaction seen when certain concentrations of 
household products are placed on the 14-day-old chorio- 
allantoic membrane and examined 3 days later on 17-day- 
old membranes. The thin white plastic ring has an 
internal diameter of 10 millimeters (0.4 inch). The area 
of injury occupies the entire plastic ring. Damaged blood 
vessels appear within the ring as an elaborate branching 
structure of pale, white, dead vessels of various sizes. 
The severity of the reaction is gauged by measuring 
the diameter of the injury, in this instance 
spanning the entire ring 
indirectly require testing and through guide- 
lines that influence testing procedures. The 
greatest amount of testing is done under laws 
administered by the Food and Drug Administra- 
tion (FDA) requiring that products be safe and ef- 
fective and that labeling claims be substantiated. 
The Environmental Protection Agency (EPA) re- 
quires testing to support pesticide registrations 
and in certain other cases. For substances other 
than pesticides, EPA relies largely on published 
literature and EPA-sponsored testing. Other agen- 
cies that use animal testing data include USD A, 
the Consumer Product Safety Commission, the Oc- 
cupational Safety and Health Administration, the 
Department of Transportation , the Federal Trade 
Commission, and the Centers for Disease Control. 
Although most laws do not explicitly require 
animal testing, requirements of safety im- 
plicitly require that the best available means 
for determining safety be used. Thus, alterna- 
tives are not likely to be used widely until they 
can be shown to be at least as valid and relia- 
ble as the tests being replaced. Meeting these 
criteria is probably not overly difficult with some 
