124 THE BLOOD 



and the thrombin so formed combines in quantitative fashion with the 

 fibrinogen to form fibrin." 



Conditions Affecting Coagulation. From the preceding discussion 

 it is evident that the rapidity of the coagulation of the blood will be 

 influenced by anything that will influence the formation of the fibrin 

 factors or their interaction. The most important influences are the 

 following: 



Temperature. Cold retards coagulation. Gentle warmth, 40 C., has- 

 tens, but a temperature above 56 C. destroys clotting, since that temperature 

 heat-coagulates the fibrinogen. 



Contact with Foreign Bodies. Such contact hastens clotting. This is 

 due to the influence of such bodies in hastening the formation of fibrin 

 factors, especially the substances that arise from the disintegration of 

 leucocytes. 



Condition of the Blood-vessel Walls. Intravascular clotting often takes 

 place upon injury of the endothelial lining of the blood vessels, either from 

 the liberation of thrombokinase in quantity too great for elimination by the 

 healthy portion of the wall (Morawitz), or by the disturbance of the equi- 

 librium of the forces which prevent the interaction of the fibrin factors 

 present in the blood (Rettger). The healthy endothelium no doubt is an im- 

 portant factor in eliminating the small amounts of the fibrin factors that must 

 be constantly forming. The open wounds and lacerations of tissue that 

 accompany the loss of blood by accident are the very conditions most favor- 

 able to clotting, since large amounts of tissue extract are set free under 

 these conditions. 



Neutral Salts. The addition of neutral salts in the proportion of 2 or 3 

 per cent, and upward delay coagulation. When added in large proportions, 

 most of these saline substances prevent coagulation altogether. Coagulation, 

 however, ensues on dilution with water. The time during which salted blood 

 can be thus preserved in a liquid state, and coagulated by the addition of 

 water, is quite indefinite. 



Oxalates and Fluorides. These and other precipitants of calcium pre- 

 vent clotting by removing this substance. 



Peptone. The injection of commercial peptone (a mixture of proteoses 

 and peptones) in the blood vessels of an animal to the extent of o . 5 gram 

 of peptone per kilo weight of the body of the animal will deprive the blood 

 of the power of coagulation. If a smaller quantity be injected the coagula- 

 tion of the blood will be delayed. If peptone blood is drawn and centri- 

 fuged, the plasma obtained is called peptone plasma. Peptone plasma in 

 the blood vessels of the animal gradually regains the power to coagulate. 

 When blood is drawn into a physiological salt solution of proteose-peptone 

 clotting occurs. 



