PROTEIN. 1025 



then becomes a hard and brittle substance ; but, like flesh, it 

 imbibes water again when moistened, and recovers its original 

 softness and elasticity. It always leaves, like albumen, when 

 burned, a portion of phosphate of lime. 



Fibrin is insoluble in alcohol, ether and water. When boiled 

 for a long time in water, particularly under pressure, its nature 

 is altered and it becomes soluble. Coagulated albumen com- 

 ports itself in the same way. Fibrin forms compounds with 

 both acids and bases. In concentrated acetic acid it swells up 

 and forms a transparent colourless jelly, which dissolves in a 

 considerable quantity of boiling water. This solution is pre- 

 cipitated by ferrocyanide of potassium. In other concentrated 

 acids fibrin undergoes a similar change. Fibrin dissolves in 

 caustic alkalies and neutralises them. It is separated from 

 them by acids, and precipitated. 



The fibrin of venous blood may be entirely dissolved in a 

 solution of nitrate of potash, although not without rubbing in a 

 mortar and digestion in the cold for some time. The solution 

 is coagulated by heat, and greatly resembles a solution of 

 albumen, (Berzelius, Scherer). This solubility in nitre is not 

 possessed by fibrin from the following sources : arterial blood, 

 the " buffy coat," and that obtained by stirring blood, nor by 

 fibrin after exposure for some time to the air, or fibrin boiled in 

 water for a few minutes, or digested in alcohol. M. Scherer 

 observes that, when in the soluble condition, fibrin is a highly 

 alterable substance, absorbing oxygen readily and emitting 

 carbonic acid ; but after being boiled for a few minutes it 

 produces no carbonic acid in an atmosphere of oxygen gas. 

 He concludes that fibrin, although always insoluble in pure 

 water, has still an uncoagulated and coagulated condition, like 

 albumen ; that it is uncoagulated in the clot of venous blood, 

 and when soluble in a solution of nitre ; but coagulated as it 

 exists in arterial blood, from the absorption, he supposes, of 

 oxygen, and after being boiled for a few minutes, or treated 

 with alcohol. The decomposition of peroxide of hydrogen, with 

 evolution of oxygen gas is occasioned, he finds, by fresh fibrin 

 from all kinds of blood, but not by boiled fibrin ; nor is the 

 decomposition- produced, it will be remembered, by coagulated 

 albumen. A solution of venous fibrin in nitre, contained in a 

 deep cylindrical jar, allows a precipitate in fine flocks to fall, 



2 x x 



