DIGESTION 



309 



Amylopsin, the sugar-forming ferment of pancreatic juice, 

 changes starch into dextrin and maltose, just as ptyalin 

 does ; but it is more powerful, and readily acts on raw 

 starch as well as boiled. 



Steapsin splits up neutral fats into glycerine 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. 



(4) Bile. Bile is a liquid the colour of which varies greatly 

 in different groups of animals, and even in the same species 

 is not constant, depending on the length of time the bile 

 has remained in the gall-bladder and other circumstances. 

 When it is recognised that the colour depends on 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. Human bile is generally described as being of a 

 reddish or golden-yellow colour, but it is doubtful whether 

 this is true of the perfectly fresh secretion, for while 

 Beaumont speaks of the yellowish bile which he could press 

 into the stomach of St. Martin by manipulating the abdomen, 

 bile flowing from a fistula has been observed to be green 

 (Robson, Copeman and Winston). That 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. This would seem to 

 indicate that human bile, originally green, may alter its 

 colour in the interval which must elapse before it can usually 

 be obtained after death. Bile, as obtained from accidental 

 fistulas in otherwise healthy persons, has a much lower 

 specific gravity than pancreatic juice (1008 to 1010). In the 

 gall-bladder water is absorbed from the bile and mucin added 

 to it, so that the specific gravity of bladder bile is as high as 

 1030 to 1040. The reaction is feebly alkaline. The composi- 

 tion of human bile from a fistula was approximately as follows : 



