Animal testing has a long history of use in medical research. Although the ethics of animal testing is a controversial issue, it is necessary for medical research. Animal research has played an important role in many of the medical advances of the last century. Animal testing offers scientists the opportunity to bring their ideas to life, from hypothesis to execution. Since 1902, almost every Nobel Prize winner related to physiology or medicine has relied on animal experimentation for their research. These research projects focused on certain animals such as rats, rabbits, guinea pigs, cows and mice. For example, Robert Koch, the 1905 Nobel Prize winner, was the first to discover that bacteria can cause infectious diseases. He proved that a parasitic microorganism caused disease by isolating the microorganism from infected tissue in a pure container. Animals can serve as models for the study of human diseases since humans and animals share hundreds of diseases. The study of animals can be applied to humans, and anesthetics, tetanus vaccine, penicillin, and insulin have been widely used in humans. Animals are the most effective objects of experimentation because they are easy to control and reproduce. However, the use of animals is more precise than other methods, and animal testing cannot be replaced or simulated because it involves uncertain factors. Sacrificing small numbers of animals can improve medical research and makes animal testing worthy and valuable. Experimental animals are protected and most countries try to minimize the pain suffered by the animal. They have regulations and laws to ensure that animals are used in the right way. Overall, animal testing is good science.