DIGESTION AND ABSORPTION IN THE INTESTINES. 



723 



stimulus was used it was necessary to cut the splanchnic some days 

 previously in order that the vasoconstrictor fibers might degenerate. 

 It seems that the secretory activity of the gland is prevented when 

 there is an interference with its blood supply. In this respect the 

 pancreas differs from the salivary glands. The secretion obtained 

 upon stimulation of the nerves is characterized, as in the case of the 

 gastric glands, by a long latent period of some minutes, a fact that 

 is explained, although not satisfactorily, on the assumption that the 

 nerve trunks stimulated contain both secretory and inhibitory fibers 

 and that the antagonistic action of the latter delays the appearance 



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32 



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Meat. 



Fig. 272. Four curves of the secretion of the pancreatic juice, the three in black, 

 from Walter, showing the secretion in dogs on different diets: (1) on 600 c.c. of milk; (2) 

 on 250 gms. bread; (3) on 100 gms. of meat. The curve in red, from Glaessner, shows 

 the secretion in man on a mixed diet, soup, meat, and bread. The figures, 1, 2, 3 etc., 

 along the abscissa indicate hours after the beginning of the meal. The figures along the 

 ordinates indicate the quantity of the secretion in cubic centimeters. 



of the secretion. These observations have been taken as proof of 

 the existence of secretory nerve fibers to the pancreas; but some 

 doubt has been thrown upon this conclusion. As is explained 

 below, all recent observers admit that the most effective stimulus 

 to the pancreas is a substance (secretin) formed in the duodenum 

 under the influence of the acid of the gastric juice. It seems possible, 

 therefore, that when the vagus is stimulated the movements of the 

 stomach that ensue may force out some acid secretion, and thus 

 indirectly lead to a stimulation of the pancreas. 



The Curve of Secretion. The rate of flow of the pancreatic 

 juice with reference to the period of digestion has been determined 

 by a number of observers. In the careful experiments reported by 

 Walter it is shown that the quantity of secretion is dependent to a 

 considerable extent upon the character of the food. Thus, the 

 flow is more abundant and reaches its maximum sooner after a 



