44 



DIGESTION 



pancreas, will be similarly related. The one apparently proved 

 example of specific adaptation of the pancreatic : juice has i not stood 

 the test of a critical examination. It was asserted that m dogs fed 

 for some days with food containing lactose (milk) the ferment 

 in that secretion, while the pancreatic mice of 



membrane, which 

 plays the part of 

 a specific chemical 

 stimulus to the 

 pancreatic cells or 

 their secretory 

 nervous mechan- 

 ism, causing them 

 to form lactase. 

 But it has been 

 conclusively shown 

 that when dogs 

 are fed with lac- 

 tose for weeks no 

 lactase appears in 

 the pancreatic 

 juice (Plimmer). 



The natural se- 

 cretion of pan- 

 creatic juice is by 

 no means so inter- 

 mittent as that of 

 saliva. In the rab- 

 bit the pancreatic, 

 like the gastric, 

 juice flows con- 

 tinuously. In the 

 dog it begins al- 

 most as soon as 



food is taken, rises in two or three hours to a maximum, then 

 falls till the fifth or sixth hour, after which it may mount again 

 somewhat, and then, gradually diminishing, ultimately stops (Figs. 

 166, 167). During normal activity the bloodvessels of the gland are 

 dilated. But under experimental conditions the increased secretion 

 caused by secretin is accompanied sometimes by an increase and 

 sometimes by a diminution in the blood- flow, and secretion may 

 continue for some time after complete cessation of the circulation, 



Flesh, 100 grm. Bread, 250 grm. 



Milk, 600 grm. 



Fig. 167. Secretion of Pancreatic Juice with Different 

 Diets (Pawlow). The hours are in roman numerals. 



