DIGESTION. 



115 



the bile-acids represent the final changes of the proteids of the liver- 

 cell. In man these acids exist in variable proportions. The bac- 

 teria of the intestinal canal break up the bile-salts. 



Glycocholic acid is a monobasic acid, crystallizing in long, fine 

 needles. Taurocholic is also monobasic; it crystallizes with great 

 difficulty, forming fine, deliquescent needles, which in solution have 

 a bitter-sweet taste. Proteid is the source of glycin and taurin. 



Subcutaneous and venous injections of bile-salts cause coma and 

 depression. 



Hay's Sulphur Test for Bile-salts. On the surface of bile or a 

 solution holding bile-salts, sprinkle flowers of sulphur; it will sink 

 to the bottom of the tube, while on most other liquids it will float. 



The bile-salts lower the surface tension of fluids in which they 

 are dissolved. 



Fig. 31. Taurin. (DuvAL.) 



Pettenkofer's Test for Bile-acids. To a nearly equal volume of 

 bile add a drop or two of syrup of cane-sugar (10 per cent.). 

 Pour concentrated H 2 S0 4 at the line of junction of the two 

 fluids, then a purple color is obtained. The purple color pro- 

 duced shows absorption bands in the spectrum. The acid on the 

 cane-sugar produces a body called furfuraldehyde, which sets up a 

 reaction with the cholalic acid to produce the color. 



The Bile-pigments. 



Normally, the color of the bile is due to the presence of but two 

 bile-pigments: bilirubin and bilwerdin. When pathological, other 

 characteristic ones have been described. Depending upon the proper- 



