COAGULATION. 



455 



of sodium chlorid. The mixture is left for forty-eight hours in a refrigerator, 

 with occasional stirring. 



2. The salt solution is drained off through cheese-cloth. 



3. The filtrate is precipitated by the addition of an equal volume of acetone, 

 and this mixture is filtered as quickly as possible through a number of small 

 filters, not using more than 50 c.c. to a filter. After the liquid has run through 

 the filters are opened, and the precipitate is spread as thin as possible with a 

 spatula. The filters are then dried rapidly in a current of cold air before an 

 electric fan. 



4. The dried filters may be kept indefinitely in a desiccator, and when 

 thrombin is needed may be extracted with a httle water, or the thrombin may 

 be extracted from the whole mass by covering the filters with water, al- 

 lowing to stand for one or two hours, and then filtering without squeezing 

 the filters. The clear solution of fibrin thus obtained may be distributed in 

 watch glasses, 1 or 2 c.c. to a glass, and be dried in front of an electric fan. 

 These dried preparations may be kept indefinitely in a desiccator. When 

 needed the contents of each glass are dissolved in 2 or 3 c.c. of water or normal 

 sahne. This preparation contains a little coagulable protein in addition to 

 thrombin. If desired this impurity may be removed by dialyzing and shaking 

 with chloroform, or by reprecipitation with acetone. 



Observations made upon preparations of thrombin purified 

 as just described show that it has the following properties: it is 

 very easily soluble in water, it is not coagulated by boiling, it is 

 precipitated with difficulty by alcohol in excess, it is precipitated 

 uninjured by half-saturation with ammonium sulphate, it responds 

 to a number of the ordinary protein tests, such as the biuret, the 

 Millon's, and especially the tryptophan (Adamkiewicz) reaction. 

 We may conclude, therefore, that in all probability thrombin is a 

 protein substance. The evidence at hand indicates that thrombin 

 as such does not exist in the circulating blood, but is present prob- 

 ably in an antecedent or inactive form known as prothrombin or 

 Ihromhogen. So far as is known this prothrombin is furnished only 

 by the blood-platelets, the bone-marrow, f and possibly the lymph- 

 glands. When the blood is shed, or under certain abnormal condi- 

 tions while circulating in the vessels, the prothrombin is changed 

 or activated to thrombin. The nature of this change is discussed 

 below. Once the thrombin exists in active condition it exhibits 

 the remarkable property of precipitating the fibrinogen in the form 

 of a gelatinous clot, the essential part of the clot being a mesh of 

 fibrin needles. 



Nature of the Action of the Thrombin on Fibrmogen.— Solu- 

 tions of fibrinogen may be precipitated readily in a number of ways, 

 but, so far as known, only thrombin is capable of precipitating it 

 in the peculiar way necessary to form a gelatinous clot. The 

 nature of this reaction is obscure. The usual view in physiology 

 is that first suggested by Schmidt, namely, that the thrombin is 

 an enzyme or ferment, fibrin ferment. If this view is correct, then, 

 in accordance with our idea of the way in which ferments act, the 



* C. K. and K. R. Drinker, "American Journal of Physiology," 41, 5, 1910. 



