THE BLOOD. 225 



semi-fluid ingredients of the blood, and to convert the whole into a 

 jelly-like, coagulated mass. 



As soon as the coagulum is formed, it begins to contract, increasing 

 in consistency as it diminishes in size. By this means the albuminous 

 liquids are pressed out from the meshes in which they were entangled. 

 They first exude upon the surface as isolated drops, which soon increase 

 in size and number. After a time they coalesce in all directions, until 

 the whole surface is covered with fluid. The clot at first adheres closely 

 to the sides of the vessel ; but as contraction goes on, it separates, and 

 fluid exudes between it and the vessel. This continues for ten or twelve 

 hours ; the clot growing constantly smaller and firmer, and the expressed 

 fluid more abundant. 



The globules, owing to their greater consistency, do not escape with 

 the albuminous fluids, but remain entangled in the coagulum. At the 

 end of twelve hours the blood is completely separated into two parts r 

 namely, the clot, a red, opaque, semi-solid mass, consisting of fibrine 

 and blood-globules ; and the serum, a transparent, nearly colorless fluid, 

 containing the watery, albuminous, and saline matters of the plasma. 



The change of the blood in coagulation may be expressed as follows : 



Before coagulation it consists of 



Fibrmlogen, 

 Albumen, 



1st. GLOBULES ; and 2d. PLASMA containing 



Paraglobuline, 



Water, 

 v Salts. 

 After coagulation it is separated into 



f Albumen, 



( Fibrine and , .. , Paraglobuline, 



1st. CLOT, containing | Globuleg . and 2d. SERUM, containing j w ^ 



[ Salts. ' 



Conditions favoring or retarding Coagulation. The coagulation of 

 blood is influenced by various physical conditions. In the first place, 

 it is suspended by a freezing temperature. If blood be drawn into a 

 narrow vessel surrounded by a freezing mixture, and rapidly cooled 

 down to C., coagulation does not occur, and the blood remains fluid 

 so long as the temperature is at this point. 



Secondly, coagulation is prevented by the presence of certain neutral 

 salts in large quantity. If fresh blood be allowed to mingle with a 

 concentrated solution of sodium sulphate, no coagulation takes place. 

 This is not because the coagulable material has been destroyed ; since, 

 if the mixture be diluted with six or seven times its volume of water, 

 so as to reduce its concentration, the fibrine solidifies in a few moments 

 as usual. 



Coagulation of the blood may be hastened or retarded by variations 

 in the manner of its withdrawal from the veins, or in the surfaces with 

 which it comes in contact. If drawn rapidly from a large orifice, it 



P 



