What gas must animals breathe to survive?

Animal must brethe to survive. The Gas that is used to survive is called OXYGEN (O2). This gas is the waste given off by plants. Another gas animals 'use' to stay alive is CARBON DIOXIDE (CO2). Yes carbon dioxide. Our breathing rate is controled by the medulla oblangata and it does so by checking the level of carbon dioxide that is present in the blood. Example. If someone is drowning and is pulled from the water and the person is not breathing it is recommended that CPR or oral resuscitation is performed. Why? The amount of CO2 that the resuscitater is breathing into the resuscitatee will trigger a reaction in the medulla oblangata that will cause the muscles of the lungs to start working again.