DIGESTION OP FOOD. 3'03 



nitric acid, containing nitrous acid, is added to bile, it under- 

 goes a series of color changes in a certain tolerably constant 

 order, becoming green, greenish-blue, blue, violet, a brick red, 

 and finally yellow ; though the green is the most characteristic 

 and permanent. Each one of these represents a distinct stage 

 of the oxidation of bilirubia, the green answering to biKverdia. 

 Such is G-melin's test for bile-pigments, by which they may be 

 detected in urine or other fluids. The absence of proteids in 

 bile is to be noted. 



The Digestive Action of Bile. — 1. So far as known, its action 

 on proteids is nil. When bile is added to the products of an 

 artificial gastric digestion, bile-salts, peptone, pepsin, and para- 

 peptone are precipitated and redissolved by excess. 3. It is 

 slightly solvent of fats, though an emulsion made with bUe is 

 very feeble. But it is likely helpful to pancreatic juice, or 

 more efficient itself when the latter is present. With free fatty 

 acids it forms soaps, which themselves help in emulsifying fat. 

 3. Membranes wet with bUe allow fats to pass mere readily; 

 hence it is inferred that bile assists in absorption. 4. When 

 bile is not poured out into the alimentary canal the faeces 

 become clay-colored and ill-smelling, foul gases being secreted 

 in abundance, so that it would seem that bile exercises an anti- 

 septic influence. It may limit the quantity of indol formed. 

 It is to be understood that these various properties of bile are 

 to be traced almost entirely to its salts ; though its alkaline 

 reaction is favorable to digestion in the intestines, apart from 

 its helpfulness in soap-forming, etc. 5. It is thought by some 

 that the bile acts as a stimulant to the intestinal tract, giving 

 rise to peristaltic movements, and also, mechanically, as a lubri- 

 cant of the faeces. In the opLuion of many, an excess of bile 

 naturally poured out causes diarrhoea, and it is well known 

 that bile given by the mouth acts as a purgative. However, 

 we must distinguish between the action of an excess and that 

 of the quantity secreted by a healthy individual. The acid of 

 the stomach has probably no effect allied to that produced by 

 giving acids medicinally, which warns us that too much must 

 not be made out of the argument from bilious diarrhaea. 6. As 

 before intimated, a great part of the bile must be regarded as 

 excrementitious. It looks as though much of the effete haemo- 

 globin of the blood and of the cholesterin, which represents 

 possibly some of the waste of nervous metabolism, were expelled 

 from the body by the bile. The cholalic acid of the faeces is 



