THE BLOOD. 



23 



watery elements of the blood to form serurn, and holds the solid 

 components, as shown by diagram as follows : 



Blood. 



Plasma. 

 I 



Corpuscles. 



Serum. 



Fibrin. 



L 



Clot. 



I 



Clotted blood. 



What is the source of the fibrin ? 



Largely, if not entirely, from the plasma. A substance known 

 as plasmine is obtained from plasma by saturation with salt, with- 

 out which there is no formation of fibrin ; and this substance redis- 

 solved readily clots and forms fibrin. Plasmine may be imitated 

 by uniting solutions of fibrinogeil and paraglobulin, obtained from 

 plasma. A third element is considered probable, and this is known 

 as the fibrin ferment : it is probably derived from the colorless 

 blood-corpuscles. There is some reason for the belief that para- 

 globulin is not an active factor in forming fibrin, but that it may 

 unite with and render inert some substance (unknown) which pre- 

 vents the formation of fibrin in the conditions of life. 



Mention some conditions which affect the coagulation of blood. 



Retard or prevent. 



Greater heat or extreme cold retard 

 or entirely check. 



Contact with living tissues, espe- 

 cially blood-vessels. 



Absence of air retards. After death 

 by asphyxia blood remains fluid ; also 

 when air is withheld from drawn 

 blood, as by film of oil. 



Agitation of vessel retards. 



More then twice the bulk of water. 



Hasten. 

 Moderate warmth, 100-120 F. 



Contact with foreign matters. 

 Access of air. 



Rest. 



Addition of moderate amounts of 

 water. 



Addition of viscid substances e. g. 

 glycerin, syrup. 



Addition of neutral salts, about 2 

 per cent, solution. 



Digestive ferments. 



Strong acids or alkalies. 



