"The proper use of anesthetics and analgesics [to reduce or eliminate pain] in research animals is an ethical and scientific imperative." The prevailing ethic incorporates the understanding that there is a wide range of pain sensation in the animal kingdom. That is, some species give strong evidence of the experience of pain and others less so. Stress, whether pain induced or not, is an equal consideration. Contemporary science incorporates the notion that an organism experiencing pain and/or stress may respond differently than one in a more normal state. This includes not only behavioral changes and differences, but physio-chemical ones as well. Scientific results obtained in a regime of pain or stress are intrinsically suspect. That is, such results bear the additional burden of proof that neither pain nor stress have a significant contribution to the results.