208 THE BILE. 



The spectrum of bile shows furthermore three absorption bands, situ- 



. / ated in the red, the orange, and the yellow. 



V The first is a dark and strongly marked band in the red, at the situa- 

 tion of the line C, but extending usually a considerable distance to the 

 left toward B. Its width varies with the thickness of the layer of fluid 

 examined, but when this is increased beyond a certain limit the whole 

 of the red disappears, so that the absorption of light at this spot is no 

 longer visible as a distinct band with red on each side of it. The band 

 itself rarely reaches the situation of the line B, and seldom or never 

 passes beyond it without extinguishing at the same time all the red 

 light of the spectrum. In layers of two or three centimetres' thickness 

 it is quite dark, often almost black, while the red on each side of it is 

 still very brilliant. 



Asa rule, the intensity of the absorption band at C is in proportion to 



L the preponderance of green in the color of the bile. Though easily seen, 



I in comparatively thin layers, in specimens of a pure green or a decided 

 greenish-olive color, it is less perceptible in specimens of a yellowish, 

 yellowish-brown, or olive-brown tint. But if a specimen of reddish or 

 yellowish-brown bile, which does not show the band distinctly, be turned 

 green by the addition of a few drops of an iodine solution, the band at 

 C at once becomes visible, often to a very marked degree. 



Fig. 69. 



A BC D 



Red Or. Yel. Green Blue Inditfo Violet 



, 



SPECTRUM OF G-KEEN (SHEEP'S) BILE. 



It would appear from this that the band at C in the spectrum of bile 

 is probably due to the presence of its green rather than its red coloring 

 matter. As the bilirubine is well known to be converted by oxidizing 

 agents into biliverdine, and as this change is accompanied by the 

 appearance of the C band when it was not previously visible, it is evi- 

 dent that the band in question belongs to the green coloring matter. 

 At the same time it is occasionally to be seen in the spectrum of dog's 

 bile which is olive-brown or even brownish-yellow in hue ; its intensity 

 in these cases being much increased by turning the bile of a decided 

 green with iodine. 



The absorption band at C is a normal characteristic of the bile, and is 

 not dependent on post-mortem changes in the secretion. We have seen 

 it distinctly marked in the spectrum of perfectly fresh sheep's bile, 



