7U PROTEIDS. [Apr. 



Fibrin, as ordinarily obtained, exhibits a filamentous structure, the 

 component threads possessing an elasticity much greater than that of 

 any other known solid proteid. 



If allowed to form gradually in large masses, the filamentous structure is not so 

 noticeable, and it resembles in this form pure india-rubber. Such lumps of fibrin 

 are capable of being split in any direction, and no definite arrangement of parallel 

 bundles of fibres can be made out. 



At ordinary temperatures fibrin is insoluble in water, being dissolved 

 only at very high temperatures, and then undergoing a complete change 

 in its characters. In hydrochloric acid solutions of 1 5 p. c. fibrin 

 swells up and becomes transparent, but is not dissolved 1 . In 'this 

 condition the mere removal of the acid by an excess of water, 

 neutralisation, or the addition of some salt, causes a return to the 

 original state. If, however, the acid be allowed to act for many days 

 at ordinary temperatures or for a few hours at 40 60 C., solution takes 

 place, and the resulting proteid is syntonin. In dilute alkalis and 

 ammonia, fibrin is much more readily soluble, though in this case also 

 the solution is greatly aided by warming; the resulting fluid contains 

 no longer fibrin, but alkali-albumin. This property is not distinctly 

 characteristic of fibrin, although it dissolves perhaps more readily in 

 both dilute acids and alkalis than do coagulated proteids. None of 

 these solutions can be coagulated on heating, which is intelligible when 

 it is remembered that they no longer contain fibrin, but either acid or 

 alkali-albumin. In addition to the above, fibrin is soluble, though with 

 difficulty and only after a considerable time, in 10 p. c. solutions of 

 sodic chloride, potassic nitrate or sodic sulphate, the solution being 

 often accompanied by putrefactive changes. These solutions may be 

 coagulated by a temperature of 60C., and are precipitated by dilution 

 with water or saturation with solid sodic chloride; in fact, by the 

 action of the neutral saline solutions the fibrin has become converted 

 into a body exceedingly like myosin or globulin 2 . 



On ignition of fibrin a residue of inorganic matter is always 

 obtained; it is, however, considered that sulphur is the only one of 

 these elements which enters essentially into its composition. In other 

 respects fibrin corresponds entirely in general composition with other 

 proteids. 



Suspended in water and heated to 70 C., it loses its elasticity, and be- 

 comes opaque ; it is then indistinguishable from other coagulated proteids. 



A peculiar property of this body remains yet to be mentioned, viz. its power of 

 decomposing hydrogen dioxide. Pieces of fibrin placed in this fluid, though them- 



1 Complete solution may however take place if the fibrin, as is frequently the 

 case, contains any adherent pepsin. 



2 Gautier, Compt. Rend. T. LXXIX. (1874), p. 227. 



