Lord Justice Moulton suggests two cases of the infliction of pain on animals for comparison. Suppose, he says, a ship to arrive in port which (as might easily happen to-day) is infested by plague-stricken rats; there are, perhaps, ten or twenty thousand rats on board. If the rats escaped and landed they might (not certainly, but probably) infect a whole city, even a much larger area, with plague, and cause death and disaster to thousands of human beings. Everyone will agree that the owner of the ship would be justified in destroying all the rats on the ship by sulphur fumes, or whatever other painful method might be necessary to prevent even one from escaping. A vast amount of suffering would be inflicted on the rats in order to prevent a far greater contingent amount of suffering. Now suppose that a man, by infecting some hundreds of rats and other animals with plague, and by trying various experiments on these animals with curative drugs, and by other operations upon them, can in all probability arrive at such a knowledge of plague and how to check it as to enable us to arrest its propagation, and so to save thousands, or even millions, of human beings from this painful and deadly disease, are we to say that this investigator must not carry on his studies, must not find out how to stop plague in future because to do so he will have to give some amount of pain to a hundred or more animals? Clearly, if we justify the shipowner we must justify the inquiries and experiments of the medical discoverer. In both cases we must hold--every sane man really does hold--that it is right to inflict pain with the expectation (not a certainty in either case, but only a reasonable probability) of preventing a far larger and more serious amount of pain in the future. It is the choice of the lesser of two evils. And thus we are led to admit that it is right that experiments and studies attended with some pain to animals should be carried on, on condition that competent and serious persons make them, for the purpose of gaining increased knowledge of the processes of life and disease. Such studies have already yielded great results--the pain in the wards of hospitals and in sick rooms is not a tenth of what it was a hundred years ago. The death-rate of great cities is a third less than it was fifty years ago. Modern medicine and modern surgery are really and demonstrably immense agencies for preventing pain and the anguish and misery which is caused by untimely death.