The text next to an image of a girl applying a cold compress reads: Using a cold pack: A cold pack removes heat from the inflammation around an injury. It also decreases the size of capillaries (small blood vessels) in the injured area, which reduces swelling and bruising. Image A has text accompanying it that reads: Inside the pack: A cold pack consists of two sealed bags, one inside the other. The strong outer bag contains solid ammonium nitrate powder. The thin-walled inner bag contains water. Part B is titled 'Squeezing the pack' and reads: When the pack is squeezed, the inner bag containing the water bursts. The water rushes into the outer bag where it dissolves the ammonium nitrate. Part C is titled 'Heat absorbed' and reads: As the ammonium nitrate dissolves, it absorbs energy from the water. This causes the temperature of the solution in the bag to drop rapidly. The pack is then ready for use.