COAGULATION, DRAWING. Coagulation. When the skin is cut, a chain reaction is triggered to stop bleeding: First, a vascular spasm, a contraction of the muscle fibers in the blood vessels, occurs to help bring the wound´s edges closer together. Then, the blood platelets form a haemostatic plug, reinforced with fibrin strands which also help emprison the red blood cells. The wound hardens upon drying and shrinks, evacuating blood serum and bringing the wound´s edges even closer together.