COLORING MATTERS. 101 



absorption band, at the junction of these colors, will account for a part 

 of this diminution ; but the spectrum is also very dim in the space 

 between the second and third absorption bands, where the normal 

 spectrum of solar light is brightest. This is the place naturally occu- 

 pied by yellow, but in the great majority of cases, in the spectrum of 

 bile, there is no pure yellow perceptible, and but little or no orange. 

 The situation of these two colors is encroached upon by the red and 

 green respectively ; and in not a few instances, as the spectrum termi- 

 nates before the commencement of the blue, the only colors really per- 

 ceptible in it are red and green. The line C in the normal spectrum 

 is situated at the junction of the red and orange, and yet the principal 

 rption band at this point, when viewed in the spectrum of bile, 

 appears to be situated entirely in the red, owing to this color taking 

 the place of the orange on the right of the line C. This peculiarity 

 shows itself in the spectrum of bile, whether the color of the specimen 

 be greenish or yellowish-brown. 



There is another spectroscopic feature in bile, due to its containing 

 more or less of two different coloring matters. 



If a tolerably thick layer of bile be placed before the spectroscope, 

 and the slit of the instrument gradually opened, the first light which 

 appears in the spectrum is usually a green light, in the latter half of 

 the space between D and E. On continuing to increase the size of the 

 opening, if the bile be deeply colored, the next to appear is a red light, 

 at the extreme end of the spectrum between A and B ; in less concen- 

 trated specimens the red light may show itself simultaneously on both 

 sides of the absorption band at C. Afterward the green light extends 

 further toward the left until the spectrum is complete. The order in 

 which these appearances follow each other depends upon the relative 

 quantity of bilirubine or biliverdiue. 



There is reason to believe that biliverdine is formed from bilirubine 

 by a process of hydration and oxidation, the elements of water entering 

 at the same time into combination. The nature of this change is shown 

 by the following formula : 



Bilirubine. Bilirerdine. 



C 16 H 13 XA -f H ; + O = CwH^O.. 



The prompt conversion of the color of ruddy or reddish-brown bile 

 into green by the action of various oxidizing agents, or even by ex- 

 posure to the air, and the evident chemical relationship between the 

 two substances, leave no doubt that this is the origin of biliverdine. 

 Both bilirubine and biliverdine are discharged with the bile into the 

 alimentary canal, where they become undistinguishable toward the 

 lower end of the small intestine. Beyond that point they are replaced 

 by the brown coloring matter of the feces, and are finally discharged 

 from the body under this form. 



5. TTrochrome. 



The coloring matter of the urine has been repeatedly studied, but 



