BLOOD. 



483 



tery of the guinea-pig or in the wing of the bat. They are precipitated 

 in enormous numbers upon threads suspended in fresh blood. They are 

 believed by Bizzozero to be the agents which immediately induce coagu- 

 lation and take part in the formation of fibrin. They become colorless 

 and disintegrate during the act of coagulation (Fig. 179). 



3. Blood-Plasma and Blood Coagulation. — Blood-plasma is blood 

 less blood-corpuscles. It may readily be obtained for study by pre- 

 venting the coagulation of horses' blood by cold, when both the red and 

 white blood-corpuscles settle to the bottom and leave the pure plasma, 

 forming a clear, amber-colored fluid above. 



Plasma is a somewhat viscid fluid of alkaline reaction. Its specific 

 gravity is about 1027 or 1028. It contains about 90 per cent, water, 

 with from 7 to 9 per cent, of various albuminoids, with small amounts 



Fiq. 179.— " Blood-Plates " and their Derivatives, after Bizzozero 

 and Laker. (Landois.) 

 1, surface view of red blood-corpuscles ; 2, side view ; 3, unchanged blood-plates ; 4, a lymph-cor- 

 puscle, surrounded with blood-plates ; 5, blood-plates variously altered ; 6, a lymph-corpuscle with two 

 heaps of fused blood-plates and threads of fibrin ; 7, group of blood-plates fused or run together ; 8, a simi- 

 lar heap of partially dissolved blood-plates with threads of fibrin. 



of urea, kreatin, kreatinin, and other nitrogenous organic bodies, as well 

 as sugar, fat, cholesterin, and mineral bodies, of which compounds of 

 sodium with chlorine and carbon dioxide are in excess. If horses' 

 plasma, prepared as above, is allowed to become warmed a few degrees 

 above the freezing point, it complete]}' solidifies into a solid mass : the 

 plasma is then said to be coagulated. This process of coagulation com- 

 mences at the edges, in contact with the walls of the vessel which con- 

 tains it, and on the free surface of the fluid, and rapidly extends through- 

 out the entire mass until a firm jelly results, which is quite as transparent 

 as the original fluid. Coagulatioiris due to certain albuminoids becoming 

 transformed from the fluid to the solid state, resulting in the formation 

 of fibrin. Shortly after the formation of the coagulum, a depression 

 forms in the upper surface of the clot, in which a clear fluid, the serum, 



