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When live animals are used in experimentation, this practice is called vivisection. (Vivisection literally means "against live cutting")(5) Animals are used in many instances because their bodies often react in a similar way to that of humans. Although animals have been used in medical research for numerous years, it was not until the early 1920's that it became more prominent. It was at this point that the introduction of using live, non-anesthetized animals to study toxic effects of an increasing array of drugs, pesticides and food additives was introduced. After this great advance in medical research the use of animals grew with leaps and bounds. In 1970 this process peaked with the use of millions of animals. In 1998 1,267,828 animals were used for medical purposes, which is more than a 50 percent decrease since 1970.(4) Although this is a drastic drop in animals used there have been many medical advances; virtually every medical break through this century has come about as the result of research with animals. .
Of the many animals used for experiments, about 90 percent are rats, mice and other rodents, while dogs, cats, and primates make up about 1 percent.(2) The animals are used to screen new drug treatments for toxicity. Animals such as mice and rats are used for two reasons; one because they are readily available upon request, and two because they are cheap, which helps aid the large cost of animals experimentation.(5) Although it has been proven, that in many cases, rats and mice are not an accurate subject to test medicines on, their popularity has only grown larger.(6) Mechanize (a travel sickness drug) caused severe deformities in rats, but not in humans, whereas Thalidomide (a sedative drug) caused no reaction in rats but cause deformities in humans.(9) This is only one of the many cases where mice and rats have been found as faulty test subjects. Dogs have a cardiovascular and respiratory system similar to that of a human.