When the liver interacts with the hydrogen peroxide, the oxygen gas it released. The hydrogen peroxide is broken down into water, and oxygen, which leads to the formation of foam as the oxygen bubbles escape the liver. The substance that interacted with liver is an enzyme as it remains unaltered. This enzyme is known as catalase. The liver can be reused to give the same reaction again with unused hydrogen peroxide, which proves that the substance in the liver (catalase) remains unaltered.
