262 THE BLOOD.. 



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 fibrinous coagulum. 

 At the end of ten or twelve hours the whole of the blood has usually 

 separated into two parts, namely, the clot, which is a red, opaque, semi- 

 solid mass, consisting of the fibrine and the blood-globules ; and the 

 serum, which is a transparent, nearly colorless fluid, containing the 

 water, albumen, and saline matters of the plasma. 



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



Before coagulation the blood consists of 



f Fibrine, 



1st. GLOBULES ; and 2d. PLASMA containing . . \ en ' 



I 



Salts. 

 After coagulation it is separated into 



1st. CLOT, containing \ . f an and 2d. SERUM, containing j Water 

 lW buleS; ' 



Salts. 



Conditions favoring or retarding Coagulation. The coagulation of 

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

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

 into a narrow vessel surrounded by a freezing mixture, so that the whole 

 of it is rapidly cooled down to (32QF.) t coagulation does not occur, 

 and the blood remains fluid indefinitely, so long as the temperature is 

 not allowed to rise above this point. A variety of other changes, such 

 as fermentation, putrefaction, and many chemical combinations or de- 

 compositions, are also prevented, as it is well known, by special condi- 

 tions of temperature. 



Secondly, the coagulation of the blood is prevented by certain of the 

 neutral salts. If fresh blood be allowed to mingle with a concentrated 

 watery solution of sodium sulphate, no coagulation takes place. This 

 is not because the coagulable material has been decomposed or chemi- 

 cally altered ; because if the mixture be diluted with six or seven times 

 its volume of water, so as to reduce the concentration of the saline solu- 

 tion, the fibrine solidifies in a few moments in the usual manner. 



Coagulation of the blood may also be hastened or retarded by varia- 

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

 with which it afterward comes in contact. If drawn rapidly from a 

 large orifice, it remains fluid for a comparatively long time ; if slowly, 

 from a narrow orifice, it coagulates quickly. The shape of the vessel 

 into which the blood is received, and the condition of its internal sur- 

 face, also exert an influence. The greater the extent of surface over 

 which the blood comes in contact with the vessel, the more is its coagu- 

 lation hastened. If the blood be allowed to flow into a tall, narrow, 

 cylindrical vessel, or into a shallow plate, it coagulates more rapidly 



