lthough an organized antivivisection movement did not begin to flourish until the second half of the nineteenth century, the increasing use of animal experimentation in the emerging science of physiolog y in the first half of the century led to heightened con-cerns about the practice, especially in Britain. The work of the French scientist Francois Magendie, one of the pioneers of the new science of physiolog y, came in for particu-lar criticism. Magendie conducted numerous experiments on living animals, often in-volving radical surgical procedures that must have caused a great deal of suffering in the days before anesthetics. A series of lecture-demonstrations by Magendie during a visit to London in 1824 created an uproar about the practice of vivisection. Even many British physicians who defended animal experimentation as a tool that could some-times be useful in biomedical research attacked Magendie for what they considered to be excessively cruel and unnecessary vivisection research.3Among those few British physicians who actively pursued experimental physiolog y during this period was Marshall Hall. His research on the phenomenon of reflex action, which involved vivisection, led to accusations of cruelty. In one instance, an attack in a medical journal on his experiments on the brain of a dog referred to the “poor tortured animal” and called vivisection experiments “horrible butcheries.”4Likely in response to the criticisms, Hall published rules for animal experimentation, perhaps the first medical investigator to do so.5 In 1835, Hall published A Critical and Experimental Essay on the Circulation of the Blood. Perhaps because of the criticism his experiments received, he began the work with an introduction on the principles of in-vestigation in physiolog y in which he directly addressed the question of the use of an-imals in research. He acknowledged the “peculiar difficulties” confronting the physi-ologist: “Unhappily for the physiologist, the subjects of the principal department of his science, that of animal physiolog y, are sentient beings; and every experiment, ev-ery new or unusual situation of such a being, is necessarily attended by pain or suffer-ing of a bodily or mental kind.