COAGULATION OF BLOOD 



217 



in fevers, or renal or thyroid disease. Low pressure is observed in 

 conditions of depression, or in muscle exhaustion, or after exhaust- 

 ing illness; in warm surroundings, etc., etc. 



Blood pressure is easily influenced by the use of drugs. For 

 example, nitro-glycerin lowers it by dilating the arterioles; strych- 

 nia raises it by contracting them; these are familiar examples. 

 Many more might be cited. 



Hemorrhage is the escape of blood in quantity, from an injured 

 vessel. Arterial hemorrhage flows in a forcible stream, bright scar- 

 let in color; if from a small vessel it will be pulsating or intermit- 

 tent in force; if from a vessel of medium size, the blood will gush 

 with a sudden spurt which carries to a rather surprising distance. 



Venous hemorrhage presents a steady flow of darker hue, rapidly 

 accumulating in a wound. 



Capillary hemorrhage is persistent oozing. 



Coagulation of Blood 



Blood which is exposed to the air at the usual temperature is 

 seen to separate into distinct portions a red, jelly-like mass and a 

 transparent straw-colored layer which is thinner. The dark mass 



FIG. 149. DIAGRAM TO ILLUSTRATE THE PROCESS OF COAGULATION, i. Fresh 

 blood, plasma and corpuscles. 2. Coagulating blood (birth of fibrin). 3. Coagu- 

 lated blood (.clot and serum). (Waller.} 



is the coagulum, consisting of fibrin with corpuscles entangled in it. 

 The fibrin is essential no fibrin, no coagulation. The straw-col- 

 ored layer above it is serum, which is plasma bereft of its fibrin and 

 corpuscles (Fig. 149). This same process may occur at the mouth 

 of a blood-vessel which has been cut or ruptured, if the stream 

 be not too forcible, and it is nature's way of stopping the flow. 



The serum, or clear, alkaline layer above the clot, contains aO 

 of the constituents of plasma except fibrin and corpuscles. 

 The proteins, sugars and fats in their various forms, in combina- 



