Dogs are regarded as faithful animals, and were probably among the first animals to be domesticated by man. But if it goes mad, it becomes very dangerous. A person who is bitten by a mad dog may die if not treated promptly and properly. A dog goes mad when it suffers from a disease called ‘rabies’. This disease is caused by a virus, which is carried in air or by some wild animals and enters the dog’s body through a wound or a cut in its skin. The virus is bullet-shaped, having a diameter of about 70 millimicrons and a length of about 210 millimicrons. When an infected animal bites a dog, the virus contained in the saliva enters the wounds and travels through sensory nerves to the central nervous system. It multiplies there and then begins to destroy the brain cells. The dog becomes lazy, suffers from fever and loses interest in food. In about 4 to 6 weeks, when these viruses affect the dog’s brain, the dog growls, barks and saliva froths from its mouth. During this period, the dog can bite anybody. This is the stage when the dog is said to be mad. It is likely to die within 3 to 5 days after these symptoms appear. Some infected dogs do not go mad but show signs of paralysis, a disease called ‘dumb rabies.’ When a mad dog bites a man, the virus present in its saliva enters the man’s body through the wound. Initially, the victim experiences mental weakness and uneasiness, which is followed by fever. He suffers from lack of sleep and feels frightened. The muscles in his throat get slackened and he faces difficulties in swallowing food or liquid. He is afraid of water, being infected by a disease called ‘hydrophobia’ which means ‘fear of water’. These signs appear in the victim within one to three months after the mad dog’s bite. In all cases of dog-bite, the affected portions should be immediately cleaned and anti-rabies injections should be given to the victim within three days of the bite, the number of injections can vary from 3 to 14 depending on the location and number of bites. The rabies virus also attacks foxes, jackals, monkeys, bats, cats and rats. Louis Pasteur introduced the treatment for rabies in 1888. The Pasteur Institute of France is a famous centre for rabies treatment.