GENERAL PHENOMENA ATTENDING COAGULATION. 67 



GENERAL PHENOMENA ATTENDING COAGULATION. 



Blood does not undergo coagulation in immediate contact with the living 

 and unaltered vessel-wall. Therefore, Bnicke was able to preserve unco- 

 agulated for eight days blood cooled to o in the still beating heart of dead 

 turtles. The blood coagulates rapidly within the dead heart or vessels 

 (but not in the capillaries) or within other channels, as, for instance, the 

 urethra. If blood stagnates in a living vessel, coagulation takes place in 

 the central axis, because it is here not in contact with the living vessel- 

 wall. Coagulation is of the greatest importance in the control of hem- 

 orrhage from injured vessels, which otherwise might terminate fatally. 

 The injured and necrotic tissues of the wound and the vessel-wall lead 

 to the formation of the occluding thrombus by coagulation. 



If the vessel-wall is altered by pathological processes, as, for instance, rough 

 or inflamed in consequence of a lesion of the intima, coagulation may take place 

 in such a situation even though the circulation be maintained". 



Coagulation of the blood is prevented or retarded: 



(a) By addition of alkalies or of ammonia, even in small amounts; 

 further, of concentrated solutions of neutral salts of alkalies and earths 

 alkaline chlorids, also sulphates, phosphates, nitrates, carbonates ; 

 disodium phosphate in 3 per cent, solution, soluble salts of calcium, 

 strontium and barium dissolved in the blood to the extent of 0.5 per 

 cent. Simultaneous addition of sodium chlorid inhibits coagulation in 

 still further degree. Magnesium sulphate i volume of a 28 per cent, 

 solution to 3^ volumes of horses' blood acts most effectively in inhibit- 

 ing coagulation. 



(b) By precipitation of the calcium by means of oxalic acid. 



Feeble acids also exert an inhibiting effect. Thus, coagulation ceases after 

 addition of acetic acid to the point of producing an acid reaction. The presence 

 of a large amount of carbon dioxid likewise retards coagulation; therefore, venous 

 blood and also the blood after asphyxiation coagulates more slowly than arte- 

 rial blood. 



(c) By addition of egg-albumin, sugar-solution, glycerin, soaps or 

 much water. If uncoagulated blood be brought in contact with a layer 

 of already separated fibrin coagulation is retarded. 



(d) Cold (o C.) retards coagulation for as long as an hour. If blood 

 be permitted to freeze at once, it will still be liquid on thawing, when it 

 undergoes coagulation. Coagulation is retarded also when the shed 

 blood is exposed to high pressure; likewise when it is brought in con- 

 tact with foreign substances to which it does not adhere, as, for instance, 

 anointed substances. 



(e) The blood of embryo birds does not coagulate at all before the 

 twelfth or fourteenth day on account of the absence of fibrin-forming 

 cells, and that of the hepatic veins but slightly. Blood from the dog 

 passed only through the heart and the lungs does not coagulate for a long 

 time. Blood from the renal vein, also blood cut off from circulation 

 through the liver and intestines, does not coagulate at all. Fetal blood 

 at the moment of birth coagulates early, but slowly, as the amount of 

 fibrin it contains is small. Menstrual blood exhibits a slighter tendency 

 to undergo coagulation if admixed with a considerable amount of alkaline 

 mucus from the genital canal. 



