40 PHENOMENA OF COAGULATION. 



The crusta is formed under other circumstances, but the cause of its formation 

 is not always clear e.f/., with increased S.G. of the corpuscles, or diminished S.G. 

 of the plasma (as in hydrsemia and chlorosis), whereby the corpuscles sink more 

 rapidly, and also during pregnancy. The taller and narrower the glass, the thicker 

 is the crusta (compare 41). The upper end of the clot, where there are few 

 corpuscles, shrinks more, and is therefore smaller than the rest of the clot. This 

 upper, lighter-coloured layer is called the ' : buffy" coat ; this, however, gradually 

 passes both as to size and colour into the normal dark-coloured clot. [Sometimes 

 the upper surface of the clot is concave or cupped. The older physicians used to 

 attribute great importance to this condition, and also to the occurrence of the 

 crusta phlogistica, or buffy coat.] 



Defibrinated Blood. If freshly-shed blood be beaten or whipped 

 with a glass-rod or with a bundle of twigs, fibrin is deposited on the 

 rod or twigs in the form of a solid, fibrous, yellowish-white, elastic- 

 mass, and the blood which remains is called " defilnnated Hood" [The 

 twigs and fibrin must be washed in a stream of water to remove 

 adhering corpuscles.] 



Coagulation of Plasma. Plasma shows phenomena exactly analogous, 

 save that there is no well-defined clot, owing to the absence of the 

 resisting corpuscles ; there is, however, always a soft, trembling jelly 

 formed, when plasma coagulates. 



Properties of Fibrin. Although the fibrin appears voluminous, it 

 only occurs to the extent of 0'2 per cent. (O'l to O3 per cent.) in the 

 blood. The amount varies considerably in two samples of the same 

 blood (Sig. Mayer). It is insoluble in water and ether; alcohol shrivels 

 it by extracting water; dilute hydrochloric acid (O'l per cent.) causes 

 it to swell up and become clear, and changes it into syntonin or acid- 

 albumin. When fresh, it has a grayish-yellow fibrous appearance, and 

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



When fresh it dissolves in 6 to 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. If, however, to a solution of fibrin in 

 0'05 per cent, soda solution, there be added acids, or (the faintly alkaline) lactate, 

 formate, butyrate, acetate, or valerianate of ammonia or soda, coagulation occurs 

 (Deutschmanu). Hydric peroxide is rapidly decomposed by fibrin (The'nard). 



According to H. Nasse, the first appearance of a coagulum occurs in man's 

 blood after 3 min. 45 sec., in woman's blood after 2 min. 20 sec. Age has no effect; 

 withdrawal of food accelerates coagulation (H. Vierordt). 



28. General Phenomena of Coagulation. 



I. Blood which is in direct contact with the living and unaltered 

 blood-vessels does not coagulate (Briicke, 1857). This important fact 

 was proved by Briicke, who filled the heart of a tortoise with blood which 

 had stood 1 5 minutes exposed to the air at 0, and kept it in a moist 

 chamber. The blood was still fluid at the end of 5^ hours, while the 



