COAGULATION OF THE BLOOD 265 



play in coagulation. The well-known observation that in thrombosis the 

 fibrin is often first formed about masses of platelets clinging to the wall 

 of the vessel indicates that they participate in the process, and Bizzozero 

 and others have maintained that the platelets and not the leucocytes are 

 the source of the prothrombin. Numerous studies on the relation of the 

 platelets to disease conditions have indicated a certain parallelism bs- 

 tween their number and the tendency to coagulation observed in the 

 various diseases (Welch). Pratt, 1 however, found that the number of 

 platelets, bore no relation to the coagulability of the blood ; and lymph, 

 which is free from platelets, will coagulate. It is, therefore, probable 

 that platelets are one, but not the sole, source of thrombin. Kemp 2 con- 

 cludes, from a thorough review of the subject, that the blood-platelets are 

 usually normal or subnormal in number during acute infectious'diseases, 

 but increase rapidly if the disease terminates by crisis ; in pernicious 

 anemia the number is always greatly diminished, although in secondary 

 anemias they may sometimes be increased ; in purpura hcemorrhagica the 

 number of plates is enormously diminished, which is perhaps related to 

 the slowness of the clotting of the blood in this condition. 



Calcium Salts. The exact significance of calcium in fibrin formation 

 is also unsettled. 8 Blood from which the calcium has been precipitated 

 will not coagulate, and the addition of calcium salts will promptly cause 

 it to do so ; furthermore, the coagulability of the blood, whether normal 

 or below normal, may be greatly increased by the administration of 

 calcium salts to the subject by mouth (Wright * ). The various hypotheses 

 advanced to explain the way in which calcium influences the clotting 

 process are not in agreement. Perhaps the most probable hypothesis is 

 that the calcium ions are necessary for the transformation of prothrom- 

 bin into thrombin (Pekelharing, Hammarsten, Morawitz), the thrombin 

 consisting of a compound of prothrombin, calcium salts, and thrombo- 

 kinase. 



Modification of Coagulability. Another important 

 matter for consideration is the effect of various substances in 

 modifying the rate or completeness of the coagulation of the 

 blood. In the first place, we have the well-known fact that if 

 blood is drawn into a glass vessel well coated with oil or vaseline, 

 through a cannula similarly protected, no coagulation will take 

 place ; but if any unoiled foreign substance enters, even particles 

 of dust, coagulation begins at once. The explanation is that 

 the leucocytes do not liberate their coagulating substances until 

 they have been injured by contact with some foreign body, and 

 the experiment proves the importance of this action of the 

 leucocytes, as well as explaining why the blood does not coagu- 

 late during life. The classical experiment of the ligation of a 

 vein without injury to the endothelium, which permits the blood 



1 Jour, of Med. Research, 1903 (10), 120. 



2 Jour. Amer. Med. Assoc., 1906 (46), 1022. 



3 See Hammarsten, Zeit. physiol. Chem., 1896 (22), 333. 



4 British Med. Jour., 1894 (ii), 57; also Boggs, Deut. Arch. klin. Med., 

 1904 (79), 539. 



