34: CHEMICAL CONSTITUENTS : FIBRIN. 



deprived of this water by drying, and then becomes a hard 

 and brittle substance ; but, like dried flesh, it imbibes water 

 again when moistened, and recovers its original softness and 

 elasticity. From the recent experiments of Dr. Richardson, 

 it appears that the coagulation of blood-fibrin depends upon 

 the escape of ammonia, being accelerated by such conditions 

 as favour the liberation of this gas, and retarded or prevented 

 by such as cause its retention in the liquid; whilst, even 

 after the clot has been formed, it may be dissolved by 

 ammonia, forming again when that gas is set free. Fibrin 

 differs from syntonin or muscle-substance in not being dis- 

 solved by very dilute muriatic acid, but being merely caused 

 to swell up into a gelatinous mass, which contracts again 

 when more acid is added. It combines with the earthy 

 phosphates, of which as much as 2^ per cent, is sometimes 

 found in the ash left by its combustion. 



18. There can be no doubt that fibrin is formed in the 

 blood and in the other fluids in which it presents itself, at 

 the expense of albumen. What is its precise destination, 

 cannot as yet be clearly specified ; but there are several 

 circumstances which point to the conclusion that it is to be 

 regarded as a transitional stage in the metamorphosis of 

 albumen into the simple fibrous tissues ( 23.) Thus, when 

 the ordinary clot of blood is examined microscopically, it is 

 found to consist, not, like an albuminous coagulum, of a 

 homogeneous mass of granules, but of a network of im- 

 perfectly-formed fibres, enclosing the red corpuscles in its 

 interstices. A much more distinct network of the same kind 

 may be seen in the colourless coagulum formed by the liquid 

 which may be skimmed off the surface of the blood drawn 

 from persons suffering under any severe inflammation*; such 

 blood coagulates slowly, and its red corpuscles and the fluid 

 in which they float have an unusual tendency to separate 

 from each other ; and the fibrin previously dissolved in the 

 latter sets into definite fibres, which continue for some days 

 to increase in firmness. It is a liquid of the same kind, 

 charged with fibrin in a peculiarly " plastic " condition, that is 

 poured forth for the formation of new tissue when the repa- 

 rative processes are at work for the healing of a wound or the 

 reunion of divided parts ; and it is by a plug of coagulated 

 fibrin, which gradually comes to present a more and jnore 



