Several circumstances concur to prevent the loss of life that would certainly occur, owing to the fluidity of the blood, when even a small vessel is divided. The first and most important of these is the almost complete closure of the opening of the tube by the contraction of the muscular tissue forming its walls. This tissue, as has been already stated, is most abundant in the small vessels which are chiefly exposed to such injuries. The closure of the vessel is of course aided by the elastic coat, which, being less and less distended, recoils as the blood pressure falls with the escape of blood from the system. Then the arteries are enclosed by a loose sheath, and when cut their proper walls retract to a considerable distance within it, leaving a narrow and tortuous passage, which impedes the exit of the blood. Again, the innermost coat of the artery is highly elastic, and has a tendency, when divided, to roll up within the artery, and thus to form a kind of valve, which is an additional obstacle to the escape of the blood. The coagulation of the blood of course plays an important part in arresting hemorrhage; a clot speedily forms in the loose tissue near the arterial or venous wound, which gradually stops up the opening and forms a plug for some distance up the vessel. Moreover, when much blood has been lost the heart beats more rapidly, indeed, but much more feebly; and with faint-ness and loss of consciousness the current of blood almost ceases. Finally, the convulsions that are the precursors of death drive the few remaining drops to the heart, and, by stimulating it to contract, afford the last chance of life being preserved.