BLOOD. 17 



BLOOD. 



Blood is an opaque fluid mass, each cubic millimeter of 

 which contains some five millions of corpuscles floating in 

 an alkaline liquid. Of these about one in 400 are colour- 

 less. In circulating bloqd the corpuscles are equally 

 distributed. Out of the living body, blood coagulates, that 

 is, separates into clot and serum ; or, if coagulation is 

 prevented by a freezing temperature, into corpuscles and 

 plasma. If blood is agitated before coagulation, the fibrin 

 is collected on the agitating surfaces, and thus separated 

 from the cruor. The coagulum varies in character accord- 

 ing to the number of corpuscles, the time occupied, and 

 the form of the recipient. It consists essentially in the 

 concretion of the plasma into a felt-work of transparent 

 fibres, each of which is scarcely a micromillimeter in width, 

 and shortens immediately after it is formed. In the circu- 

 lating blood coagulation is prevented by the influence 

 upon it of the living tissues, with which it is in relation. 

 If blood is received into non-contaminated vessels, coagu- 

 lation is delayed or prevented. It is not dependent on the 

 access or escape of any gas or vapour. It is indefinitely 

 deferred at o C, most accelerated at 40 C. By subsidence 

 at about 6 C. blood separates into plasma and corpuscles, 

 of which the weights in normal human blood are nearly 

 equal. It contains three albuminous substances, viz. : (i) 

 common albumin ; (2) a little alkali-albumin ; and (3) the 

 substance which becomes fibrin. Plasma coagulates at 

 ordinary temperatures, becoming gelatinous if diluted, 

 yielding a fim clot of fibrin if concentrated. The substance 

 which thus assumes the solid form is called, in its dissolved 

 state, plasmin, or the substratum of coagulation. It has 

 the properties of a globulin. Two kinds of globulin exist in 

 the plasma, one, named fibrinogen, in very small quantity 

 (0*3 per cent.), which disappears in the act of coagulation ; 

 the other, which is much more abundant, and may consti- 



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