PHENOMENA OF COAGULATION. 41 



heart itself still continued to beat. He observed that at the blood 

 was uncoagulated in the contracting heart of a tortoise after eight days. 

 Blood inside a contracting frog's heart preserved under mercury does 

 not coagulate. If the wall of the vessel be altered by pathological pro- 

 cesses (e.g., if the intima becomes rough and uneven, or undergoes 

 inflammatory change) coagulation is apt to occur at these places. 

 Blood rapidly coagulates in a dead heart, or in blood-vessels (but not 

 in capillaries) or other canals (e.g., the ureter) (Virchow). 



If blood stagnates in a living vessel, coagulation begins in the central 

 axis, because here there is no contact with the wall of the living blood- 

 vessel. This influence of the wall of blood-vessels was, to some extent, 

 known to Thackrah (1819) and to Sir Astley Cooper. 



II. Conditions which Hinder or Delay Coagulation. (a.) The 

 addition of small quantities of alkalies and ammonia, or of con- 

 centrated solutions of neutral salts of the alkalies and earths (alkaline 

 chlorides, sulphates, phosphates, nitrates, carbonates). Magnesic 

 sulphate acts most favourably in delaying coagulation (1 vol. solution 

 of 28 per cent, to 3^ vol. blood of the horse). 



(&.) The precipitation of the fibrinoplastin by adding weak acids, or 

 by C0 2 . 



By the addition of acetic acid until the reaction is acid, the coagulation is com- 

 pletely arrested. A large amount of C0 2 delays it, and hence venous blood 

 coagulates more slowly than arterial. Hence, also, the blood of suffocated persona 

 remains fluid. 



(c.) The addition of egg-albumin, syrup, glycerine, and much water. 

 If uncoagulated blood be brought into contact with a layer of already- 

 formed fibrin, coagulation occurs later. 



(d.) By cold at coagulation may be delayed for one hour 

 (J. Davy.) If blood is frozen at once, after thawing, it is still fluid, 

 and then coagulates (Hewson). When shed blood is under high 

 pressure it coagulates slowly (Landois). 



(e.) Blood of embryo-fowls does not coagulate before the 12th or 14th 

 day of incubation (Boll); that of the hepatic rein very slightly; 

 menstrual blood shows little tendency to coagulate when alkaline mucus 

 from the vagina is mixed with it. If it be rapidly discharged, it 

 coagulates in masses. 



(/.) Blood rich in fibrin from inflamed parts coagulates slowly. In "bleeders " 

 (haemophilia), coagulation seems not to take place, owing to a want of the sub- 

 stances producing fibrin ; hence, in these cases, wounds of vessels are not plugged 

 with fibrin. Albertoni observed that if tryptic pancreas ferment (dissolved in 

 glycerine), be injected into the blood of an animal, blood does not coagulate. 

 Schmidt-Mulheim found that after the injection of pure peptone into the blood 

 (0'3 to 0'6 grammes per kilo.) of a dog, the blood lost its power of coagulating. 

 A substance is formed in the plasma, which prevents coagulation, but which is 



