BILE SECRETION. 173 



bodies, give under this treatment a similar color, in 

 order to make the reaction a trustworthy test for bile 

 salts, the two characteristic bands given by the spectro- 

 scope should also be observed. 



The following is said to be a more characteristic test : 

 Rinse out a porcelain capsule successively with the fluid 

 to be tested, then with weak sulphuric acid, and finally 

 with a weak solution of sugar, then heat to 70 C., when 

 the capsule turns purple. 



2. Gmelin's test for the bile pigments depends upon the 

 fact that, during the stages of oxidation, the bili- 

 rubin undergoes a series of changes in color which fol- 

 low the sequence of the familiar solar spectrum. Place 

 a few drops of the fluid to be tested on a white surface 

 (a capsule or plate), and allow a drop of nitric acid, 

 yellow with nitrous acid fumes, to run into it; as they 

 mingle together the rainbow-like play of color appears. 

 This, when watched, will be found to consist of a series 

 of changes to green, blue, violet, red, and yellow. 



The same can be observed by allowing the acid to 

 trickle gently down the side of a test-tube fixed in an 

 inclined position so that it cannot be shaken, the play 

 of color can then be seen starting from the point of 

 junction of the two fluids. 



METHOD OF SECRETION OF BILE. 



The secretion of the liver varies less in the amount formed in 

 a given time than that of other digestive glands. Although the 

 changes in the rate of its secretion are not so marked, they fol- 

 low the same general rule as those of other glands, i.e., after 

 food is taken there is a sudden rise, then a gradual fall, followed 

 by a second rise in the amount produced, as is so well seen in the 

 case of the pancreas. Although hunger is said to check the 

 secretion of bile, it is practically continuous, as is the activity of 

 all glands whose duty it is to eliminate noxious substances. 



At the end of a period of fasting the gall-bladder is always 



