THE BILE. 207 



with a color of its own, when viewed by the more refrangible rays of 

 the solar spectrum. If a specimen of bile, of a clear greenish color, be 

 placed in the track of either the violet or blue rays of the solar spec- 

 trum, it becomes visible with a light yellowish-green tint. In the green 

 it is more yellowish ; and in the yellow it has a distinct tinge of red ; 

 while in the red ray its fluorescence is hardly perceptible. Thus in all 

 parts of the spectrum where it exhibits this property, it emits a light 

 of less refrangibility than that of the ray by which it is illuminated. 

 The property of fluorescence is also manifested, to a remarkable degree, 

 by solutions of chlorophylle, which, although of a clear green color by 

 diffused daylight, are of a pure red, when viewed by either the violet, 

 blue, green, or yellow rays of the spectrum. 



The fluorescence of bile, however, does not depend altogether upon 

 its coloring matter, but is due mainly to the presence of the biliary salts, 

 since it is exhibited in an equal degree by watery or alcoholic solutions 

 of sodium taurocholate and glycocholate ; the only difference being that 

 the color of these solutions by the violet and blue rays is nearly pure 

 yellow instead of yellowish-green. 



Thirdly, the spectrum of bile is distinguished by certain peculiar 

 characters and absorption bands, dependent upon its coloring matter. 1 

 All the more refrangible rays are absorbed with great intensity, so that 

 the visible spectrum is very short, terminating usually within the limits 

 of the green, about midway between the lines E and F. A portion of 

 the green, accordingly, and the whole of the blue, indigo, and violet are 

 completely absorbed, even when the bile 'is viewed in a layer only one 

 centimetre in thickness. In dog's and pig's bile the spectrum some- 

 times terminates in the first half of the green, at or just beyond the 

 situation of the line E ; and in human bile even within this point, about 

 the commencement of the green part of the spectrum. 



Another peculiarity of the spectrum of bile is that its light does not 

 fade away gradually toward the more refrangible portions, as is the ^ 

 case with most other colored fluids, but it terminates suddenly, so that 

 the light is cut off abruptly at the situations above mentioned, thus 

 making a strong contrast with the complete darkness immediately 

 beyond its limits. This peculiarity is perceptible in bile of all shades 

 of green, olive, yellow, or reddish-brown. 



1 If any colored fluid be placed before the slit of a spectroscope, so that the 

 light which passes through it is afterward dispersed by the prism of the instru- 

 ment, to form a spectrum, it is found that it absorbs the light of the different 

 colors with different degrees of intensity. When the absorption of light in any 

 particular part of the spectrum is so strong as to cause at that spot a decided 

 dimness in comparison with the neighboring regions, it is called an " absorption 

 band," and is characteristic of the fluid which produces it. The situation of an 

 absorption band is usually indicated by reference to Frauenhofer's lines of the 

 solar spectrum, known as A, B, C, D. E, F, G, and H. 



