THE COAGULATION OF THE BLOOD 221 



Some persons, who are known as bleeders, exhibit a decided tend- 

 ency toward delayed clotting which frequently endangers their life 

 (hemophilia). Hemorrhages from the mucous surfaces may occur 

 almost at any time and without apparent cause. Extravasations 

 may also result into the subcutaneous tissue and the joints, as well as 

 into the different serous cavities of the body. This condition, the cause 

 of which is unknown, is inherited and usually destroys the male line, 

 i.e., it remains dormant in the females but may be transferred by 

 them to their male offsprings. 



CONDITIONS INFLUENCING THE COAGULATION TIME 



Temperature. In general it may be said that high temperatures 

 accelerate and low temperatures retard the clotting. For this reason, 

 hot cloths are often applied to bleeding surfaces, the heat acting merely 

 as an agent to intensify the chemical changes underlying the process 

 of coagulation. Conversely, a sample of blood may be retained in its 

 fluid condition for a relatively long period of tune by surrounding the 

 receptacle in which it is kept with crushed ice. This result may be 

 made the more striking if blood is used, the normal clotting time of 

 which is long; for example, that of the horse or that of invertebrates. 

 If blood is heated to 60 C., it loses its power of coagulation, because 

 the fibrinogen is precipitated at this temperature. 



The effect of heat and cold seems to be directly proportional to the 

 destruction of the thrombocytes, but while these elements disintegrate 

 more readily at high than at low temperatures, they are also broken 

 up at the temperature of the body. The fact that the blood of cold- 

 blooded animals clots very slowly is frequently cited as proving that 

 low temperatures tend to retard the coagulation, but it is more than 

 likely that this is merely a coincidence and that the correct explanation 

 is to be sought in fundamental differences in the manner of clotting 

 of this type of blood. 1 



Methods of Collecting the Blood. If the blood is drawn into a. 

 receptacle with a smooth surface, it does not clot so readily as if col- 

 lected in one possessing a rough surface. It is also true that the coagu- 

 lation sets in more quickly in a receptacle which presents a large area 

 to the blood. For this reason, the clotting may be greatly retarded 

 by oiling the walls of the vessel or by coating them with wax, paraffin, 

 or agar. In explanation of these differences it need only be mentioned 

 that the liberation of the activating agent depends primarily upon the 

 destruction of the thrombocytes. Quite naturally, an oiled receptacle 

 or one possessing a small surface, must be less injurious to these cells 

 than one presenting the opposite characteristics. 



The same explanation holds true in the case of blood which is 

 retained in its fluid state by surrounding it with the normal lining of 

 the blood-vessel. Thus, if a certain segment of a vein is filled by 



1 L. Loeb, Archiv path. Anat., clxxxv, 1906, 160. 



