CHEMICAL PROCESSES IN THE INTESTINE. 511 



cellulose undergoes a fermentation in the intestine by the action of micro- 

 organisms, producing marsh-gas, acetic acid, and butyric acid, has 

 been especially shown by TAPPEINER; still it is not known to what extent 

 the cellulose is destroyed in this way. 1 



The bile has, as shown by MOORE and ROCKWOOD 2 and then espe- 

 cially by PFLUGER, the property to a high degree of dissolving fatty 

 acids, especially oleic acid, which itself is a solvent for other fatty acids, 

 and hence, as will be seen later, it is of great importance in the absorp- 

 tion of fat. It is also of great importance that the bile, as previously 

 stated, not only activates the steapsinogen, but that, as first shown by 

 NENCKI and RACHFORD, 3 it accelerates the fat-splitting action of the 

 steapsin. According to v. FURTH and ScmJTZ 4 the bile-salts are the 

 active constituents of the bile in this cleavage, and the fatty acids set 

 free can combine with the alkalies of the intestinal and pancreatic juices 

 and the bile, producing soaps which are of great importance in the 

 emulsification of the fats. 



If to a soda solution of about 1-3 p. m. pure, perfectly neutral 

 olive-oil is added in not too large a quantity, a transient emulsion is 

 obtained after vigorous shaking. If, on the contrary, one adds to the 

 same quantity of soda solution an equal amount of commercial olive- 

 oil (which always contains free fatty acids), the vessel need only be 

 turned over for the two liquids to mix, and immediately there appears 

 a very finely divided and permanent emulsion, making the liquid appear 

 like milk. The free fatty acids of the commercial oil, which is always 

 somewhat rancid, combine with the alkali to form soaps which act to 

 emulsify the fats (BRUCKE, GAD, LOEWENTHAL 5 ) . This emulsifying 

 action of the fatty acids split off by the pancreatic juice is undoubtedly 

 assisted by the habitual occurrence of free fatty acids in the food, as 

 well as by the splitting off of fatty acids from the neutral fats in the 

 stomach (see page 476). 



Bile completely prevents peptic zymolysis in artificial digestion. 



1 On the digestion of cellulose see Henneberg and Stohmann, Zeitschr, f . Biologic, 

 21, 613; v. Knieriem, ibid., 67; Hofmeister, Arch. f. wiss. u. prakt. Thierheilkunde, 

 11; Weiske, Zeitsehr. f. Biologic, 22, 373; Tappeiner, ibid., 20 and 24; Mallevre, 

 Pfliiger's Arch., 49; Omeliansky, Arch. d. scienc. biol. de St. Petersbourg, 7; E. Miiller, 

 Pfliiger's Arch., 83; Lohrisch, Zeitschr. f. physiol. Chem., 47 (literature); Pringsheim r 

 ibid. 78, 266 (1912). 



2 Proceedings of Roy. Soc., 60, and Journ. of Physiol., 21. In regard to Pfliiger's 

 work see Absorption. 



3 Nencki, Arch. f. exp. Path. u. Pharm., 20; Rachford, Journal of Physiol., 12. 



4 Centralbl. f . Physiol., 20. 



5 Briicke, Wien, Sitzungsber., 61, Abt. 2; Gad, Arch. f. (Anat. u.) Physiol., 1878; 

 Loewenthal, ibid., 1897. 



