INFLUENCE OF NERVOUS SYSTEM ON DIGESTIVE GLANDS 407 



a solution of the residue containing the secretin still evokes a rapid 

 secretion of bile. The fact that the same hormone excites the 

 formation both of pancreatic juice and bile is obviously related \o 

 that common action of the two juices in digestion on which we have 

 already dwelt. 



When food passes into the stomach, there is at once a sharp rise in 

 the rate of secretion of bile. A maximum is reached from the fourth 

 to the eighth hour that is, while the food is in the intestine. There 

 is then a fall, succeeded by a second smaller rise about the fifteenth 

 or sixteenth hour, from which the secretion gradually declines to its 

 minimum. Upon the whole, the curves of secretion of pancreatic 

 juice and bile show a fairly close correspondence, except that the 

 latter is more nearly continuous. But when we compare the curves 

 representing the rate at which the bile actually enters the intestine 

 with the curve of pancreatic secre- 

 tion (Fig. 160), we are struck by 

 their almost absolute parallelism. 

 This lends additional support to 

 the conclusion 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 products of digestion of 

 egg-white produce a copious discharge. This discharge may be 

 determined by the relatively large amount of acid chyme passed 

 through the pylorus when proteins are digested in the stomach and 

 the stimulus to the formation of secretin occasioned 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 thems -Ives. An increased 



Fig. 169. Pancreatic Juice and Bile 

 (Paw low). The upper curves repre- 

 sent the hourly rate of pancreatic 

 secretion, and the lower the rate at 

 which the bile enters the intestine; 

 a, a', milk diet; b, b', meat; c, c f , 

 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. 



