266 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



therefore, upon the general statement that the bile-acids stimulate the epithe- 

 lial cells to a greater activity in the absorption of fat, or possibly accomplish 

 the same end in some more indirect way as yet undiscovered. It was formerly 

 believed that bile is also of great importance in restraining the processes of 

 putrefaction in the intestine. It was asserted that bile is an efficient antiseptic, 

 and that this property comes into use normally in preventing excessive putre- 

 faction. Bacteriological experiments made by a number of observers have 

 shown, however, that bile itself has very feeble antiseptic properties, as is 

 indicated by the fact that it putrefies readily. The free bile-acids and cholalic 

 acid do have a direct retarding eifect upon putrefactions outside the body; 

 but this action is not very pronounced, and has not been demonstrated satis- 

 factorily for bile itself. It seems to be generally true that in cases of biliary 

 fistula the feces have a very fetid odor when meat and fat are taken in the 

 food. But the increased putrefaction in these cases may possibly be due to 

 some indirect result of the withdrawal of bile. It has been suggested, for 

 instance, that the deficient absorption of fat which follows upon the removal 

 of the bile results in the proteid and carbohydrate material becoming coated 

 with an insoluble layer of fat, so that the penetration of the digestive enzymes 

 is retarded and greater opportunity is given for the action of bacteria. We 

 may conclude, therefore, that while there does not seem to be sufficient warrant 

 at present for believing that the bile exerts a direct antiseptic action upon the 

 intestinal contents, nevertheless its presence limits in some way the extent of 

 putrefaction. Lastly, bile takes a direct part in suspending or destroying 

 peptic digestion in the acid chyme forced from the stomach into the duodenum. 

 The chyme meeting with bile and pancreatic juice is neutralized or is made 

 alkaline, which alone would prevent further peptonization. Moreover, when 

 chyme and bile are mixed a precipitate occurs, consisting partly of proteids 

 (proteoses and syntonin) and partly of bile-acids. It is probable that pepsin, 

 according to its well-known property, is thrown down in this flocculent pre- 

 cipitate and, as it were, prepared for its destruction. 



Glycogen. One of the most important functions of the liver is the for- 

 mation of glycogen. This substance was found in the liver in 1857 by Claude 

 Bernard, and is one of several brilliant discoveries made by him. Glycogeu has 

 the formula (C 6 H 10 O 5 ) n , which is also the general formula given to vegetable 

 starch ; glycogen is therefore frequently spoken of as " animal starch." It 

 gives, however, a port-wine-red color with iodine solutions, instead of the 

 familiar deep blue of vegetable starch, and this reaction serves to detect glyco- 

 gen not only in its solutions, but also in the liver-cells. Glycogen is readily 

 soluble in water, and the solutions have a characteristic opalescent appearance. 

 Like starch, glycogen is acted upon by amylolytic enzymes, and the end- 

 products are apparently the same namely, maltose, or maltose and some dex- 

 trin. For a more complete account of the chemical reactions of glycogen, and 

 for the methods of obtaining it from the liver, reference must be made to the 

 Chemical section. 



Occurrence of Glycogen in the Liver. Glycogen can be detected in 



