DIGESTION 



385 



elusion deduced from their chemical and physical properties, 

 that in digestion they are partners in a common work. 



While the rate at which bile passes into the intestine seems to 

 be influenced by digestion much in the same way as the rate 

 of pancreatic secretion, the details are as yet less exactly known. 

 In the fasting animal no bile enters the gut. When food is taken 

 the flow begins after a definite interval, which varies for the 

 different kinds of food. As long as digestion lasts bile continues 

 to escape, but both the quantity and quality depend upon the 

 nature of the food. Water, raw egg-white, and starch paste, 

 whether given by the mouth or introduced directly into the 

 stomach of a dog, 

 cause no flow of 

 bile. But fat, the 

 extractives of 

 meat, and the pro- 

 ducts of digestion 

 of egg-white pro- 

 duce a copious dis- 

 charge. This dis- 

 charge may be de- 

 termined by the 

 relatively large 

 amount of acid 

 chyme passed 

 through the py- 

 lorus when pro- 

 teins are digested 

 in the stomach 

 and the stimulus 

 to the formation 

 of secretin occa- 

 sioned by the 

 presence of this 



chyme or of fatty material in the duodenum. In the case of 

 fat a further favourable influence on the secretion of bile is 

 the absorption of bile-salts which accompanies the absorption 

 of the fatty acids and soaps produced in fat digestion. Bile- 

 salts stimulate the secretion of bile, including bile-salts them- 

 selves. An increased flow of bile-salts into the intestine acceler- 

 ates the splitting of fats by the pancreatic juice, and therefore 

 the absorption of bile-salts acting as solvents for, or chemically 

 united to, the fatty acids and soaps. A circle analogous to the 

 ' vicious circle ' of the logicians, but constituting a physiological 

 adaptation of most potent virtue in the digestion of fats, is thus 

 established. Not only is the quantity of bile poured into the 



25 



FIG. 152. PANCREATIC JUICE AND BILE (PAWLOW). 



The upper curves represent the hourly rate of pan- 

 creatic secretion, and the lower the rate at which the 

 bile enters the intestine ; a, a', milk diet ; b, V, meat ; 

 c, c', bread. Only the general form of the curves is to 

 be compared. The scale of the ordinates of the various 

 curves was not the same. 



