COAGULATION. 467 



it follows that in all probability the neutral salts exert a restraining 

 effect on the process of clotting because they prevent or retard the 

 activation of the prothrombin by the calcium. 



4. By the Action of Oxalate Solutions. If blood as it flows from 

 the vessels is mixed with solutions of potassium or sodium oxalate 

 in proportion sufficient to make a total strength of 0.1 per cent, 

 or more of these salts, coagulation is prevented entirely. Addi- 

 tion of an excess of water does not produce clotting in this case, 

 but solutions of any soluble calcium salt quickly start the process. 

 The explanation of the action of the oxalate solutions is simple; 

 they are supposed to precipitate the calcium as insoluble calcium 

 oxalate. 



5. By the Action of Sodium Fluorid. Blood drawn directly into 

 a solution of sodium fluorid does not clot. It is best to use a 3 per 

 cent, solution of the fluorid, and to take 1 part of the solution 

 to 9 parts of blood. Addition of thrombin to this fluorid 

 blood causes clotting, while calcium salts are usually stated to be 

 without effect. As a matter of fact, calcium salts cause a pre- 

 cipitate of a portion of the protein, and if added cautiously in 

 excess they induce clotting, as in the case of the oxalated blood. 

 The fluorid plasma may be made to clot also by dialysis. We 

 may believe that the fluorid, like the oxalate, prevents clotting 

 by removing the calcium. The calcium is not precipitated, but is 

 held bound as a fluorid in combination with a portion of the 

 protein (Rettger). Coagulation is prevented in a similar way by 

 solutions of sodium citrate or sodium metaphosphate. In the 

 case of the citrate use a 2 per cent, solution and take 1 part to 4 

 of the blood. 



6. By the Injection of Certain Organic Substances. There are a 

 number of substances which when injected into the blood retard 

 or prevent its coagulation. For instance, solutions of ordinary 

 preparations of pepsin, trypsin, peptone, snake venom, leech 

 extracts, etc. Snake venom may be wonderfully potent in this 

 particular; it is stated that so little as 0.00001 gm. to each kilogram 

 of animal suffices to destroy the coagulability of the blood. Of 

 these various bodies solutions of peptone have received the most 

 attention from investigators. Peptone, as usually obtained by 

 digestion experiments, is in reality a mixture of prot oses and 

 peptones. When injected into the circulation in the proportion of 

 0.3 gm. to each kilogram of animal the coagulability of the blood is 

 very greatly diminished for a brief period of half an hour or more. 

 When, however, such solutions are added to freshly drawn blood 

 they exercise no influence upon the coagulation. Evidently, 

 therefore, when injected into the blood they provoke a reaction of 

 some sort, the products of which prevent coagulation. There is 



