COAGULATION OF THE BLOOD. 719 



by a feeble coagulation. The internal conditions which retard coagu- 

 lation, are certain inflammatory states of the system, perfect smooth- 

 ness of the interior of the heart and bloodvessels, and, above all, a 

 healthy condition of their lining membrane. 



Although rest, as when drawn blood is set aside, is favorable to co- 

 agulation, and moderate agitation, as when the blood is gently shaken, 

 in a bottle, delays this act, it is remarkable that stirring blood rapidly 

 with a rod, or whipping it with a bundle of sticks or wires, causes the 

 fibrin quickly to coagulate in thready masses on the rod; this is the 

 usual method of defibrinating blood, which afterwards remains fluid, or 

 forms but a very soft imperfect second coagulum. The effect of whipping 

 depends on the rapid and frequent contact of the multiplied surfaces 

 of the wires with the blood. Again, a temperature varying from 100, 

 or the natural temperature of the blood, up to 120, accelerates coagu- 

 lation, but a greater heat retards it; at 150 this property of the 

 fibrin is said to be permanently destroyed, whilst, above that tempera- 

 ture, the albumen of the blood itself coagulates. When blood is al- 

 lowed to cool, its coagulation is retarded in proportion to the degree 

 of cold to which it is subjected; at 27J, or 4J below the freezing- 

 point of water, it solidifies; and if it has not been previously allowed 

 to coagulate, and the freezing process is rapidly completed, it will co- 

 agulate on being thawed. The coagulating property is, therefore, 

 proportionally, sooner destroyed by an elevation than by a lowering 

 of the temperature of the blood; moreover, frozen blood may be pre- 

 served for a long time, and yet retain its power of coagulating when 

 thawed. The influence of exposure to air, in accelerating the coagu- 

 lation of the blood, probably explains the corresponding effects of the 

 slow escape of the blood from the vessels, and of its reception into 

 shallow basins. These conditions do not act by lowering the tempera- 

 ture, for that would retard coagulation, nor by the escape of the halitus 

 merely; but it has been suggested that they operate by favoring the' 

 escape of ammonia from the blood. All conditions which facilitate 

 the escape of vapor or gas from the blood, certainly favor its coagu- 

 lation. Thus, coagulation occurs in a vacuum, a fact which shows that 

 the presence of air is not necessary, a condition too which would favor 

 the escape of ammonia; but it also occurs, and even more quickly, 

 when the blood is subjected to increased atmospheric pressure. Com- 

 plete exclusion from air, though it retards, does not prevent coagula- 

 tion, as blood will at last coagulate in closed vessels, and even within 

 the dead body shut up from the air. The rapid escape of blood from 

 its vessels, and its reception into deep glasses or basins, are supposed 

 to retard coagulation, by affording less opportunity of exposure of the 

 blood to the air. Of all the circumstances which hasten the formation 

 of the clot, the multiplication of the points of contact with solid bodies 

 seems to be the most potent; the smallest particle of thread suffices to 

 induce rapid coagulation, where, in the absence of any foreign body, a 

 much slower process of clotting would have occurred. Blood received 

 into metal or earthenware utensils, is said to coagulate sooner than 

 when received into glass vessels, perhaps owing to difference of rough- 

 ness of the surface. The accelerating effect of slight dilution and the 



