58 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



in the red close to the line C. Heat the solution, after adding; 

 some tin and hydrochloric acid, in a flask on the water-bath. 

 The solution turns yellowish-red and when examined spec- 

 troscopically shows a dark band, usually not sharply defined, 

 between the green and the blue, similar to that of urobilin. 

 Sometimes, however, only a diffuse darkening in that part of 

 the spectrum is apparent. 



The same pigment appears to be present sometimes in 

 urine ; at least many urines show similar absorption phenom- 

 ena. 



(6) BLOOD-FIBRIN. 

 I. Conduct towards 0.27 per cent. Hydrochloric Acid. 



Pour on a few shreds of fresh fibrin or fibrin kept in 

 glycerin, after it has been well washed) some 0.27 per cent, 

 hydrochloric acid (3 cc. of hydrochloric acid, sp. gr. 1.19, to 

 500 cc. of water). The fibrin swells gradually and dissolves 

 on long digestion at 40 with the formation of acid albumin. 

 This precipitates on neutralizing with sodium carbonate solu- 

 tion. 



II. Conduct towards Hydrogen Peroxide. 



Pour on a few shreds of fresh fibrin some hydrogen perox- 

 ide solution: evolution of oxygen. Repeat the experiment 

 with boiled fibrin: no gas is evolved. The action of the 

 fibrin on the hydrogen peroxide is probably due to the pres- 

 ence of leucocytes in the fibrin. 



III. Conduct towards Salts. 



Fresh fibrin swells and gradually dissolves more or less 

 completely in a solution of potassium nitrate. 



(c) BLOOD-SERUM. 



The blood-serum, as well as the serous fluids, contains a 

 proteid soluble in water, serum albumin, and one insoluble 



