THE DIGESTIVE SYSTEM. 319 



toluidin blue, and an inner, filled, in the resting stage of the gland, with 

 secretory granules. The granules stain well with osmic acid, eosin, or 

 neutral gentian. 



After a prolonged period of secretory activity the granules are 

 greatly diminished in number, and the inner zone of the cell is relatively 

 and absolutely smaller as compared with the outer zone. Under normal 

 conditions this diminution of the inner zone does not occur, because the 

 formation of new granules keeps pace with the extrusion of those 

 previously formed, so that the appearance of the cells is little altered 

 by the secretion required for an ordinary meal. The secretory granules 

 are in all probability zymogenic, and represent the precursors of the 

 enzymes found in the juice. In the case of trypsinogen, the precursor 

 has received the name of protrypsinogen. 



THE BILE. 



The bile is not a digestive juice in the same sense in which saliva and 

 the gastric and pancreatic juices belong to that category. It is to be 

 looked upon as an excretion, which incidentally assists the digestive 

 action of the pancreatic juice. The production of bile is constant, 

 although the rate of formation varies with the period of the day and 

 other circumstances, and, as it is formed, the secretion is stored in the 

 gall-bladder. This reservoir discharges the accumulated bile into the 

 intestine simultaneously with the great flow of pancreatic juice, which 

 takes place during the third hour of digestion of a meal. The 

 mechanism by which this emptying of the gall-bladder is effected has 

 not yet been definitely ascertained. 



THE COMPOSITION OF THE BILE. 



Bile may be obtained for analysis from the gall-bladder of a recently 

 killed animal, or it may be collected from a gall-bladder fistula during 

 life. Its composition, however, is not the same in the two cases, fistula 

 bile being more dilute than bile which has been stored for a time in 

 the gall-bladder, The difference is shown in the following' two analyses 

 of human bile by different observers : 



Fistula Bile. Gall-bladder Bile. 



Mucin and pigments . 0'148 



Sodium taurocholate . 0*055 



Sodium glycocholate . 0'165 



Cholesterol 



Lecithin . . . 0'038 



Fats 



Inorganic salts . . 0'840 



Water 98'7 



Mucin . . . .1-29 

 Sodium taurocholate . . 0*87 

 Sodium glycocholate . . 3-03 

 Cholesterol . . . 0'35 

 Lecithin .... 0'53 



Fats 0-73 



Soaps . . . .1-39 



