COAGULATION OF THE BLOOD 27 



The relative proportions of serum and clot are variable, unless that 

 portion of the serum retained between the meshes of the coagulated 

 mass is included in the estimate. As the clot is composed of corpuscles 

 and fibrin, and as these in their moist state represent, in general terms, 

 about one-half of the blood, it may be stated that after coagulation, the 

 actual proportions of clot and serum are about equal. Simply taking 

 the serum that separates spontaneously, there is a large quantity, when 

 the clot is densely contracted, and a smaller quantity, when it is loose 

 and soft. Usually the clot retains about one-fifth of the serum. 



On removing the clot, after the separation of the serum is complete, 

 it presents a gelatinous consistence, and is more or less firm according 

 to the degree of contraction. As a general rule, when coagulation has 

 been rapid, the clot is soft and but slightly contracted. When, on the 

 other hand, coagulation has been slow, the clot contracts for a long time 

 and is much denser. When coagulation is slow, the clot frequently 

 presents what is known as the buffed and cupped appearance. 



Blood flowing slowly from a small opening in a vessel coagulates more 

 rapidly than when it is discharged in a full stream from a large opening. 

 If received into a shallow vessel, it coagulates much more rapidly than 

 in a deep vessel. If the inner surface of the vessel is rough, coagula- 

 tion is more rapid than when it is smooth and polished. If the blood as 

 it flows is received on a cloth or a bundle of twigs, it coagulates almost 

 instantaneously. In short, it appears that conditions that f ayor eyapora- 

 tion from the blood hasten its coagulation. 



Coagulation of the blood is prevented by rapid freezing, but it occurs 

 afterward if the blood is carefully thawed. Between 32 and 140 Fahr. 

 (o and 60 C.), elevation of temperature increases the rapidity of 

 coagulation. 



Various chemical substances retard or prevent coagulation. Among 

 these may be mentioned potassium and sodium hydrate, sodium carbo- 

 nate, ammonium carbonate, potassium carbonate, ammonia, and sodium 

 sulphate. In the menstrual flow the blood remains liquid on account of 

 mixture with the abundant secretions of the vagina. 



The blood coagulates in the vessels after death, though less rapidly 

 than when drawn from the body. It occurs in twelve to twenty-four 

 hours after circulation has ceased, and the blood then is found chiefly in 

 the venous system. The existence of projections into the calibre of 

 vessels or the passage of a fine thread through an artery or vein will 

 determine the formation of a small coagulum on the foreign substance, 

 while the circulation is neither interrupted nor retarded. In the present 

 state of knowledge, explanation of these facts is difficult if not impos- 

 sible. The process, under these conditions, cannot be subjected to direct 



