2l8 PHYSIOLOGICAL CHEMISTRY. 



formed be cut out it will be found that the contained blood 

 will remain fluid some hours or days even. This shows that 

 contact with living walls is not the element preventing coagu- 

 lation. 



Apparently blood exists normally in a very peculiar condi- 

 tion of equilibrium, in which not one but several factors are 

 concerned. The same may be said of the equilibrium of many 

 salt solutions. Changes of temperature, the addition of for- 

 eign bodies in traces even, stirring, pouring from one vessel 

 into another, or contact with the dust particles of the air in 

 the one case as in the other may iaduce a change. In the 

 living vessels of the body as well as after leaving the body 

 the equilibrium may be destroyed and a coagulation take place. 

 This is illustrated in the intravascular clotting after wounds in 

 which the vessels as a whole may not be impaired; injury to 

 the lining endothelium results in throwing foreign particles 

 into the blood stream sufficient to induce clotting or coagu- 

 lation. 



EXPERIMENTAL ILLUSTRATIONS. 



Some of the simpler phenomena connected with the coagu- 

 lation of blood may be readily shown by experiment. 



Ex. Have ready two test-tubes. Pour into the first one cc. of a cold 

 saturated solution of sodium sulphate, the other is left clean and dry. De- 

 capitate a rat and allow two cc. of the escaping blood to flow into the 

 tube containing the sodium sulphate. The rest of the blood is collected 

 in the dry tube. In a very few minutes coagulation takes place in the lat- 

 ter tube, while it is prevented by the sodium sulphate in the former. 



Allow both tubes to stand at rest a day or two. In the salted tube it 

 will be noticed that most of the corpuscles have settled to the bottom, leav- 

 ing a clear and lighter colored liquid, while in the other tube the coagulum 

 has begun to shrink into a smaller mass, from which droplets of yellowish 

 serum ooze. The corpuscles in this remain with the fibrin. 



Ex. Collect a quantity of slaughter-house blood by running two vol- 

 umes of the latter into one volume of saturated solution of sodium sul- 

 phate. Shake the mixture and allow it to stand at a low temperature sev- 

 eral days. Coagulation does not occur, but a gradual precipitation of the 

 corpuscles is observed, leaving a yellowish liquid known as salted plasm^ 

 which may be poured off and used for various experiments. 



Ex. Pour a few cc. of the salted plasma into a test-tube and dilute it 

 with several times its volume of water. On slight warming of the mix- 



