THE CHEMISTRY OF THE DIGESTIVE JUICES 363 



on raw starch as well as boiled. Pancreatic amylase is mainly, 

 perhaps entirely, present in the juice in the form of active ferment. 

 If a zymogen stage exists, the mother-substance is less stable or less 

 easily extracted from the gland than is trypsinogen. In this respect 

 amylase also resembles ptyalin. A small amount of maltase is 

 contained in pancreatic juice, and further hydrolyses to dextrose a 

 portion of the maltose formed by the amylase. 



Steapsin or pancreatic lipase splits up neutral fats into glycerin and 

 the corresponding fatty acids. The latter unite with the alkalies of 

 the pancreatic juice and the bile to form soaps. In this important 

 process bile acts as the helpmate of pancreatic juice; together they 

 effect much more than either or both can accomplish by separate 

 action. Many tissues contain fat-splitting ferments or Upases, some 

 of which are perhaps identical with the pancreatic lipase. The lipase 

 exists as active ferment in the pancreatic j uice, but there is reason 

 to believe that a portion of it may be present as a zymogen in the 

 gland, and probably in the secretion as well. It is changed Jnto 

 active ferment by the bile salts. Active lipase can also be extracted 

 from the pancreas by glycerin or water. It is to be noted that it is 

 only the proteolytic enzyme which is totally inactive till it reaches 

 the intestine. The significance of this will be discussed later on. 



Bile. Bile is a liquid the colour of which varies in different groups 

 of animals, and even in the same species is not constant, depending 

 on the length of time the fluid has remained in the gall-bladder and 

 other circumstances. When it is recognized that the colour is due 

 to a series of pigments, which are by no means stable, and of which 

 one can be caused to pass into another by oxidation or reduction, 

 this want of uniformity will be easily intelligible. The fresh bile of 

 carnivora is golden-red. The bile of herbivorous animals is in 

 general of a green tint, but, when it has been retained long in the 

 gall-bladder, may incline to reddish-brown. Fresh human bile, as 

 it flows from a fistula just established, is of a reddish-brown, golden- 

 yellow or yellow colour. Beaumont speaks of the yellowish bile 

 which he could press into the stomach of St. Martin by manipulating 

 the abdomen. In a case observed by the writer, it was seen that 

 when the bile flowing from a fistula was allowed to spread out in a 

 dressing, it became greenish, because of oxidation of a part of the 

 bilirubin to biliverdin, although as it actually escaped from the fistula 

 it was yellow. The bile of a monkey taken from the gall-bladder 

 immediately after death is dark green, but if left a few hours in the 

 gall-bladder it is brown, the green pigment having been reduced. It 

 should be remembered that human bile from the post-mortem room 

 may alter its colour in the interval which must elapse before it can 

 usually be procured after death. Bile, as obtained from fistulse in 

 otherwise healthy persons, has a specific gravity of about 1008 to 

 lo 10. In the gall-bladder water is absorbed from the bile and 



