CHAP, i.] BLOOD. 19 



it apart from paraglobulin, and then freed from ferment by repeated 

 washing, will yield a solution not spontaneously coagulable, but 

 clotting freely on the addition of ferment only. In favour of 

 the view that the presence of paraglobulin is essential may be 

 quoted the striking fact that certain specimens of hydrocele fluid 

 may be met with which will not coagulate either spontaneously or 

 upon the addition of ferment alone, but will coagulate upon the 

 addition of paraglobulin and ferment. Such fluids may be supposed 

 to contain fibrinogen only. And it has been argued that two 

 substances have been confused under the name of fibrinogen : one 

 coagulating at the same temperature as paraglobulin, and needing 

 the cooperation of paraglobulin to form fibrin ; and another body, 

 which may be thrown down from solutions of plasm ine or from 

 blood at the temperature of 55 60 (the fluids thereby losing the 

 power of coagulating), and which is fibrinogen already on its way 

 to become fibrin, in fact a sort of nascent fibrin, capable of becoming 

 actual fibrin in the total absence of paraglobulin. Lastly tbell 

 presence_of a neutral salt, such as sodium chloride, appears to be 

 essential to the process, coagulation not occurring even where all , 

 three factors are present, if no neutral salt accompanies them. 



Awaiting further investigation we may for the present conclude 

 that fibrin is formed by the conversion, through the agency of 

 a ferment, of a substance fibrinogen, which forms part of the 

 plasm ine spoken of above, but the exact nature of that conversion 

 and whether paraglobulin has any share in the matter, and if so 

 what, must remain as yet undecided. 



This conception of coagulation as a chemical process between 

 certain factors renders easy of comprehension the influence of 

 various conditions on the coagulation of blood. The quickening 

 influence of heat, the retarding effect of cold, the favourable action 

 of motion and of contact with surfaces, and hence the results 

 of whipping and the influence exerted by the form and surface of 

 vessels, become intelligible. The greater the number of points, 

 that is the larger and rougher the surface presented by the vessel 

 into which blood is shed, the more quickly coagulation comes on, 

 for contact with surfaces favours chemical union. So also the 

 presence of spongy platinum, or of an inert powder like charcoal, 

 quickens the coagulation of tardily clotting fluids, such as many 

 specimens of pericardia! fluid. 



Having thus arrived at an approximative knowledge of the 

 nature of coagulation, we are in a better position for discussing the 

 question, Why does blood remain fluid in the vessels of the living 

 body and yet clot when shed ? 



The older views may be at once summarily dismissed. The 

 clotting is not due to loss of temperature, for cold retards coagu- 

 lation, and the blood of cold-blooded animals behaves just like that 

 of warm-blooded animals in clotting when shed. It is not due to 

 loss of motion, for motion favours coagulation. It is not due to 



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