QUESTION 546. _When does bleeding from a wound become dangerous?_ _Answer._ Profuse bleeding is always dangerous, but it should be remembered that bleeding occurs from two sources: first from the arteries, which are the vessels which convey the blood _from_ the heart, and second from the veins, through which the blood flows back to the heart. The first is called _arterial_ bleeding and the second _venous_ bleeding. Now it must be remembered that the heart is the great force-pump of the body, and that it supplies all parts of the body with blood, somewhat as the feed-pump of a locomotive supplies the boiler with water. The arteries referred to fulfill the same purpose that the feed-pipe does to a locomotive pump--they convey the fluid from the pump to the place where it is needed. Now the blood is forced into these arteries with a certain amount of pressure, so that if any of them are cut or injured the blood will flow out in a jet or spurt just as the water will escape from a feed-pipe if that is ruptured. The blood which flows through the veins back to the heart may, on the other hand, be compared to the water in the supply pipes of a locomotive pump, that is, there is very little pressure on it, and therefore if they are injured the flow of blood from them is less rapid than from the arteries. It will therefore be seen that arterial bleeding is much more dangerous, because the blood flows from them under a pressure. QUESTION 547. _How can arterial bleeding be distinguished from venous bleeding?_ _Answer._ The blood is of a bright scarlet color, and is forced out in successive jets; each jet corresponds with the movements of the heart. This characteristic spurting is caused by the intermittent force-pump action of the heart, driving out the blood. Venous bleeding is distinguished from arterial by the dark-blue color of the blood when flowing from the wound. It never flows in repeated jets, but oozes slowly from the wounded surfaces. Venous blood is traveling toward the heart, and there is consequently little force behind to cause a more rapid flow. This form of bleeding is comparatively harmless, unless occurring from very large veins.[118] [118] “Emergencies and How to Treat Them,” by Joseph W. Howe, M. D. QUESTION 548. _How can the bleeding be stopped in case an artery is cut or ruptured?_