COAdULATIOX or THE BLO(Jj 317 



most rapidly with fil)rinofrcn of Ijlood of tlio species from wliicli tiiey are ob- 

 tiiiiu'd.'-'' Jii some iiistanci's this spccilicity is ahsoliito, hut inoie jieiieraliy ( par- 

 ticuhirly in tlio maiiuiuilia ) it is only relative. J.oeh also found tliat tiie amount 

 of tissue ooaj>ulin was not decreased in or<;ans altered by phospliorus jioisoning, 

 althou^di duriufj experimental autolysis the coajrulins disajjpear. Wiien tissue 

 coagulins and blood coaiiulins act together, the elTect is greater than the sum 

 of their independent actions, indicating the probability that they combine in 

 some way to [jroduce a particularly active coagulin. The blood eoagulins are 

 (piite dili'erent from the tissue eoagulins in many important respects, and the 

 eoagulins cannot be l(M)ked ujion as a single substance of dillVrcnt origins. 



Blood-platelets. — It is still undetennined just what jiart the platelets ])lay 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 ve.ssel 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 in- 

 dicated a certain parallelism l)et\veen their number and the tendency to coagulation 

 observed in the various diseases (Welch). Howell I)elieves the platelets to be 

 the chief source of thromboplastin, which neutralizes the antithrombin of the 

 blood and tims causes clotting. Eordet and Delange consider the ])latelets of 

 more importance than the leucocytes in producing participant* of the coagulat- 

 ing mechanism. The histological evidence of the importance of the ])latelets in 

 thrombus formation is conclusive (see Zurhelle, Derewenko), and Cramer and 

 Pringle -« state that coagulation cannot occur without platelets. Kemp 29 con- 

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

 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 lurmorhagica the number of plates is enormously di- 

 minished, which is perhaps related to the slowness of the clotting of the i)lood 

 in this condition. Duke 3'^ states that when the i)latelet count falls below 10,(100 

 per cubic mm. there is delayed coagulation and a tendency to purpura : with 

 counts above 40,000 tliere is usually no hemorrhagic tendency. If the platelet 

 count is reduced artificially (by benzene, diphtheria toxin) a similar purpuric 

 tendency is observed. Poisons that in large doses reduce the platelet count, will 

 increase it if in small doses. 



Calcium Salts. — The exact significance of calcium in fibrin formation is still 

 imsettled. Blood from which the calcium has been precipitated will not coagu- 

 late, and the addition of calcium salts v'\\\ promptly cause it to do so. The vari- 

 ous hypotheses advanced to explain the way in which calcium influences the 

 clotting process are not in agreement. One hypothesis is tliat the calcium ions 

 are necessary for the transformation of prothrombin into thrombin (Pekelharing, 

 Hammarsten, IMorawitz), the thrombin consisting of a compoimd of prothrombin, 

 calcium salts, and thrombokinase. Howell considers that no kinase is necessary, 

 the calcium activating the prothrombin whenever it is not inhibited by anti- 

 thrombin. 



Modification of Coagulability. — Another important matter for 

 consideration is the etit'eet of various substanees in moclifyin<>- 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 ]n-otected, 

 no coagulation will take place ; but if any unoiled foreign stibstance 

 enters, even particles of dust, coagulation begins at once. The ex- 



20 Leo Loeb, Univ. of Penn. Med. Bull.. 1004 (16), .3S2 ; Muraschew. Deut \rch 

 klin. Med., 1904 (SO). 187. 



28 Quart. Jour. Exper. Physiol., 1913 (6), 1 



29 Jour. Amer. ^Med. Assoc., in06 (46). 1022. 



30 Jour. Exp. Med., 1011 (14). 265; Arch. Int. :\red., 1012 (10). 44.1: Jour 

 Amer. Med. Assoc, 1915 (65), 1600. 



