Explanation

Edward Jenner (1796), an English physician prepared the first vaccine when he injected the fluid from the sore of milkmaid suffering from cowpox into the body of a healthy boy which when exposed later to smallpox, exhibited resistance to the disease. Louis Pasteur (1879) found that ageing cultures of cholera bacteria were too weak to cause disease, when injected into chickens. But chickens injected with these cultures became immune of fowl-cholera. By using this method, Pasteur developed a vaccine against rabies in 1885.