GENERAL PHENOMENA OF COAGULATION. 3 1 



Coagulation of Plasma. Plasma shows phenomena exactly analogous, save that 

 the clot is not so well marked, owing to the absence of the resisting corpuscles; 

 there is, however, always a soft trembling jelly formed when plasma coagulates. 

 [In Hewson's experiment on the blood of a horse tied in a vein, he found that the 

 plasma coagulated fibrin being formed, so that he showed coagulation to be due to 

 changes in the plasma itself ( 29).] 



Properties of Fibrin. Although the fibrin appears voluminous, it only occurs 

 to the extent of 0*2 per cent. (O'l to 0'3 per cent.) in the blood. The amount 

 varies considerably in two samples of the same blood. It is insoluble in water and 

 ether; alcohol shrivels it by extracting water; dilute hydrochloric acid (0*1 p er 

 cent.) causes, it to swejl u p and become jglear. and changes it into syntoniu or acid- 

 albumin ( 249, III.). When fresh, it has a greyish-yellow fibrous appearance, 

 and is elastic ; when dried, it is horny, transparent, brittle, and friable. 



When fresh it dissolves in 6-8 per cent, solutions of sodium nitrate or sulphate, in dilute 

 alkalies, and in ammonia, thus forming alkali-albuminate. Heat does not coagulate these 

 solutions. [It is also soluble in, or rather decomposed by, 5-10 per cent, solutions of neutral 

 salts, e.g., NaCl, yielding two hbro-globulins (Green).] Hydric peroxide is rapidly decomposed 

 by fibrin into water and ( Thenard). Fibrin which has been exposed to the air for a long time 

 is no longer soluble in solution of potassic nitrate, but in neurin (Mauthner). During putre- 

 faction it passes into solution, albumin being formed. Fibrin contains, entangled in it, ferric, 

 calcic, and magnesic phosphates, and calcium sulphate whose origin is unknown. 



Time for Coagulation. The first appearance of a coagulum occurs in man's blood after 3 

 minutes 45 seconds, in woman's blood alter 2 min. 20 sec. (H. Nasse). Age has no effect; with- 

 drawal of food accelerates coagulation (H. Vierorclt). 



28. GENERAL PHENOMENA OF COAGULATION. I. Blood in direct 

 contact with living unaltered blood-vessels does not coagulate. [Hewson 

 (1772) found that when he tied the jugular vein of a horse in two places, and 

 excised it, the blood did not coagulate for a long time.] Brlicke filled the heart 

 of a tortoise with blood which had stood 15 minutes exposed to the air at 0, 

 and kept it in a moist chamber ; at C. the blood was still uncoagulated in the 

 contracting heart after eight days. Blood in a contracting frog's heart preserved 

 under mercury does not coagulate. If the wall of the vessel be altered by 

 pathological processes (e.g., if the intima becomes rough and uneven, or under- 

 goes 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). 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. 



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

 small quantities of alkalies, ammonia, or concentrated 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 3J vols, blood of the horse). 



(b) Precipitation of the fibrino-plastin by adding weak acids, or C0 2 . 



By the addition of acetic acid until the reaction is acid, coagulation is completely arrested. 

 A large amount of C0 2 delays it, hence venous blood coagulates more slowly than arterial, and 

 the blood of suffocated persons remains fluid for the same reason. 



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

 coagulated blood be brought into contact with a layer of already-formed fibrin, 

 coagulation occurs later. 



(d) By cold (0 C.) coagulation may be delayed for one hour. 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. 



(e) Blood of embryo-fowls does not coagulate before the twelfth or fourteenth day 

 of incubation (Boll) ; that of the hepatic vein very slightly ; menstrual blood shows 



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