14 CHEMICAL COMPOSITION' OF HUMAN BODY. 



viously coagulated, and the solution has a beautiful purple 

 or blue colour. 



Fibrin is found most abundantly in the blood and the 

 more perfect portions of the lymph and chyle. It is very 

 doubtful, however, whether fibrin, as such, exists in these 

 fluids, whether, that is to say, it is not itself formed at 

 the moment of coagulation. (See Chapter on the Blood.) 



If a common clot of blood be pressed in fine linen while 

 a stream of water flows upon it, the whole of the blood- 

 colour is gradually removed, and strings and various pieces 

 remain of a soft, yet tough, elastic, and opaque-white sub- 

 stance, which consist of fibrin, impure, with a mixture of 

 fatty matter, lymph-corpuscles, shreds of the membranes 

 of red blood-corpuscles, and some saline substances. Fibrin 

 somewhat purer than this may be obtained by stirring blood 

 while it coagulates, and collecting the shreds that attach 

 themselves to the instrument, or by retarding the coagula- 

 tion, and, while the red blood-corpuscles sink, collecting 

 the fibrin unmixed with them. But in neither of these 

 cases is the fibrin perfectly pure. 



Chemically, fibrin and albumen can scarcely be distin- 

 guished ; the only difference apparently being that fibrin 

 contains 1*5 more oxygen in every 100 parts than albumen 

 does. Mr. A. H. Smee has, indeed, apparently converted 

 albumen into fibrin, by exposing a solution to the prolonged 

 influence of oxygen. Nearly all the changes, produced by 

 various agents, in coagulated albumen, may be repeated 

 with coagulated fibrin, with no greater differences of result 

 than may be reasonably ascribed to the differences in the 

 mechanical properties of the two substances. Of such dif- 

 ferences, the principal are, that fibrin immersed in acetic 

 acid swells up and becomes transparent like gelatin, while 

 albumen undergoes no such apparent change ; and that 

 deutoxyde of hydrogen is decomposed when in contact with 

 coagulated fibrin, but not with albumen. 



Casein, which is said to be albumen in combination with 



