CONTROL OF HEMORRHAGE 2 19 



The time required for coagulation is a matter of some im- 

 portance from the clinical standpoint. The average normal co- 

 agulation time of undisturbed blood is from two to four minutes 

 for the beginning of the process and seven to eight for its com- 

 pletion; these figures vary under certain circumstances. If the 

 blood is received in a cool vessel without disturbance, coagulation 

 takes place slowly, the corpuscles sink in the plasma, the red cells 

 (being heavier) falling to the bottom while the white ones form a 

 reddish gray layer immediately above, or a "buffy coat," as it is 

 called, so that the clot appears in layers. Blood from inflamed 

 tissues coagulates after this manner. 



Does blood ever coagulate without exposure to the air; that is, 

 within the vessels of the living body? Yes, in certain abnormal 

 conditions. If the lining of the vessel wall is diseased or rough- 

 ened, or injured as by application of ligatures, or in the presence 

 ^of bacteria, or when a foreign body is floating in the blood stream, 

 these all favor coagulation within the vessels. High body 

 temperature and various chemical substances have a similar effect, 

 the presence of oxygen as well, or the admission of air. 



If air finds it way into a vessel forming an air embolus, there is danger that 

 it will induce coagulation uppn reaching the uneven surfaces of the heart if 

 not before. This is an unusual accident, but a possible one, consequently 

 great care should be exercised when filling and using a hypodermic syringe. 

 (The double accident of piercing a vein and injecting air would have to occur 

 in order to do harm of this sort.) 



Arterial blood coagulates more easily than venous. A stationary clot within 

 a vessel is a thrombus; a moving clot is an embolus. A portion of a thrombus 

 may be swept off in the stream as an embolus and, lodging at some distant 

 point, will become a thrombus there. 



Clinical note. Phlebitis is inflammation of a vein. The blood within 

 the vein coagulates, and the vein feels like a hard cord. 



Coagulation does not occur in the blood of the capillaries nor 

 within perfectly normal vessel walls in health, nor in blood with a 

 deficiency of calcium salts. 



A dot within a blood-vessel resembles the true coagulum but is not 

 identical with it, being largely composed of platelets with fewer threads of 

 fibrin. The white clot found in the heart at autopsy is mostly fibrin. 



Control of hemorrhage. Nature's way is by coagulation at 

 the mouth of the vessel. To favor this, we seek to i. slow the 

 current: by rest, by elevation of the bleeding part, by compression 



