The study of the biological effects of foreign chemicals (whether therapeutic drugs or chemicals present at work or in the environment) interests the biologist from a number of different and complementary viewpoints. Apart from the more obvious pharmacological and toxicological interest, the experimentalist often uses foreign chemicals to produce in experimental animals disease states similar to naturally occurring diseases, so that their pathogenetic mechanisms and therapy can be studied under controlled conditions. In addition - as Claude Bernard pointed out over a century ago - foreign...