346 A MANUAL OF PHYSIOLOGY 



high-pressure salivary glands rather than with the low- 

 pressure pancreas. But although the biliary pressure is high 

 relatively to that of the blood with which the secreting cells 

 are supplied, it is absolutely very low ; and this is a point of 

 practical importance, for a comparatively slight obstruction 

 to the outflow, even such as is offered by a congested or 

 inflamed condition of the duodenal wall about the mouth 

 of the duct, may be sufficient to cause reabsorption of the 

 bile through the lymphatics, and consequent jaundice. Of 



course, complete plugging of the 

 duct by a biliary calculus is a 

 much more formidable barrier, 

 and inevitably leads to jaundice, 

 just as ligature of a salivary duct, 

 in spite of the great secretory 

 pressure, inevitably causes oedema 

 of the gland. 



When food passes into the 

 stomach, there is at once a sharp 



rise in the rate of secretion of 

 FIG. 109. RATE OF SECRETION , ., . . , , r 



OF BILE. hue. A maximum is reached from 



S shows how the rate of secretion the fourth to the eighth hour 



of bile falls in a dog when a biliary ,1 , i M ,1 r j ,LI_ 



fistula is first made, and the bile that IS, while the food IS in the 



thus prevented from entering the inf^tin-. th PTV > ic fVmn a fall cn^ 



intestine ; P shows the fall in the l - sune > l 1S tn en a tail, SUC 



percentage of solids. The numbers ceeded by a second smaller rise 



along the horizontal axis are J 



quarters of an hour since bile began about the fifteenth Or sixteenth 



to escape through the fistula. The , r , i_ ,t_ 



numbers along the vertical axis refer nOUr, from Which the SCCretlOH 



only to curve S, and represent the rrr^ (\\-\i\\\i rl^olinoc f/^> ifo m i n i n m 

 rate of secretion in arbitrary units. Squally declines tO its minimum. 



Upon the whole, the curves of 



secretion of pancreatic juice and bile show a fairly close 

 correspondence, which lends additional support to the view 

 derived from their chemical and physical properties, that in 

 digestion they are partners in a common work. 



We do not know in what way the rate of secretion of bile 

 is influenced by digestion, although it has been conjectured 

 that the first abrupt rise may be started by reflex nervous 

 action, and that later on absorbed food products may directly 

 excite the hepatic cells. Rutherford found that when the 

 mucous membrane of the stomach and duodenum is irritated 



