What factors are responsible for blood clotting outside of the body, for example in the case of an injury, and not internally?
Platelets are tiny red cells that flow with in our bodies to assist with our injuries. When we cut ourselves, blood flows with the cut and this carries platelets. The platelets combine with the oxygen in the air and the platelets disintegrate to form a thread-like substance called fibrin. Fibrin acts like a dam and holds the further flow of blood