COAGULATION. 435 



pure blood-plasma. The cooling probably prevents clotting by 

 keeping the corpuscles intact. 



2. By the Action of Neutral Salts. Blood received at once from 

 the blood-vessels into a solution of such neutral salts as sodium 

 sulphate or magnesium sulphate, and well mixed, does not clot. In 

 this case also the corpuscles settle slowly, or they may be centri- 

 fugalized, and specimens of plasma be obtained. For this purpose 

 horses' or cats' blood is to be preferred. Such plasma is known 

 as " salted plasma "; it is frequently used in experiments in coag- 

 ulation, for example, in testing the efficacy of a given ferment 

 solution. The best salt to use is magnesium sulphate in solutions 

 of 27 per cent. : 1 part by volume of this solution is usually mixed 

 with 4 parts of blood; if cats' blood is used a smaller amount may 

 be taken 1 part of the solution to 9 of blood. Salted plasma 

 or salted blood again clots when diluted sufficiently with water or 

 when ferment solutions are added to it. How the salts prevent 

 coagulation is not definitely known possibly by preventing the 

 disintegration of corpuscles and the formation of ferment, possibly 

 by altering some later stage in the process. 



3. 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. Ad- 

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

 but solutions of some 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. 



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

 a solution of sodium fluorid (1 part of a 3 per cent, solution of 

 sodium fluorid to 9 parts of blood) does not clot. Addition of 

 calcium salts alone to such a mixture fails to provoke clotting, but 

 addition of solutions of thrombin, or of calcium and zymoplastic 

 substance, will provoke coagulation. The plasma obtained by 

 centrifugalizing a mixture of blood and sodium fluorid gives, 

 therefore, a means of testing for the presence of thrombin (Arthus) . 



5. 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 



