QUANTITY OF BLOOD. 423 



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 forms, 

 therefore, an excellent means of testing 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 

 digestion experiments, is in reality a mixture of proteoses 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. When, however, such solutions are added 

 to freshly drawn blood they exercise no influence upon the coagu- 

 lation. -Evidently, therefore, when injected into the blood they 

 provoke a reaction of some sort the products of which prevent 

 coagulation. Delezenne's work given above offers a simple ex- 

 planation. Such solutions cause a rapid destruction of leucocytes 

 (and blood plates) with the production of leuconuclein and histon ; 

 the former substance is destroyed or removed by the liver and the 

 histon remaining in the blood is the cause of the non-coagulation. 

 Pick and Spiro * have shown that this action of peptone solutions is 

 not due to the peptone or the albumoses contained in it. When 

 obtained in purified form these substances have no such effect. 

 They attribute the action to a substance, derived probably from 

 the tissues used in the preparation of the peptone, and for which 

 they suggest the name of peptozym. Leech extracts differ from 

 solutions containing peptozym in that they prevent the clotting 

 of the blood when added to it outside the body. They evidently 

 contain already formed a substance whose action prevents coagula- 

 tion. This substance is secreted by the salivary glands of the leech. 

 It has been extracted from the glands in a more or less pure form, 

 and is designated as hirudin. Nothing is known regarding its 

 chemical structure or its mode of action in preventing clotting. 



Total Quantity of Blood in the Body. The total quantity of 

 blood in the body has been determined approximately for man and 

 a number of the lower animals. The method used in such determi- 

 nations consists essentially in first bleeding the animal as thoroughly 

 * "Zeitschrift f. physiol. Chemie," 31, 235, 1900. 



