BILE SECRETION. 181 



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

 the capsule turns purple. 



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

 fact that, during the stages of oxidation, the bilirubin 

 undergoes a series of changes in color which follow 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 

 found greatly distended, because the secretion has continued to 

 flow into that receptacle, and there has been no call for its dis- 

 charge into the duodenum. 



The amount of bile produced by dogs is much influenced by 

 the diet. It is very great when meat alone is consumed, less 

 with vegetable diet, and very small with a diet of pure fat. As 

 a general rule, the bile is more abundantly produced in herbiv- 

 orous than in carnivorous animals. 



