342 THE HUMAN BODY. 



duodenum. If oil be shaken up with water, the two can- 

 not be got to mix; immediately the shaking ceases the oil 

 floats up to the top; but if some raw egg be added, a creamy 

 mixture is readily formed, in which the oil remains for a 

 long time evenly suspended in the watery menstruum. 

 The reason of this is that each oil-droplet becomes sur- 

 rounded by a delicate pellicle of albumen, and is thus pre- 

 vented from fusing with its neighbors to make large drops, 

 which would soon float to the top. Such a mixture is called 

 an emulsion, and the albumin of the pancreatic secretion 

 emulsifies the oils in the chyle, which becomes white (for the- 

 same reason as milk is that color) because the innumerable 

 tiny oil-drops floating in it reflect all the light which falls 

 on its surface. 



In brief, the pancreatic secretion converts starch inta 

 sugars; dissolves proteids (if necessary) and converts them 

 into peptones; emulsifies fats, and, to a certain extent,. 

 breaks them up into glycerine and fatty acids; the latter 

 are then saponified by the alkalies present. 



The Bile. Human bile when quite fresh is a golden 

 brown liquid; it becomes green when kept. As formed in 

 the liver it contains hardly any mucin, but if it makes any 

 stay in the gall-bladder it acquires a great deal from the 

 lining membrane of that sac, and becomes very "ropy."' 

 It is alkaline in reaction and, besides coloring matters, min- 

 eral salts, and water, contains the sodium salts of two nitro- 

 genized acids, taurocholic and glychochotic, the former pre- 

 dominating in human bile. 



Pettenkofer's Bile Test. If a small fragment of cane 

 sugar be added to some bile, and then a large quantity of 

 strong sulphuric acid, a brilliant purple color is developed, 

 by certain products of the decomposition of its acids; the 

 physician can in this way, in disease, detect their presence- 

 in the urine or other secretions of the Body. Gmeliris 

 Bile Test. The bile-coloring matters, treated with yellow- 

 nitric acid, go through a series of oxidations, accompanied 

 with changes of color from yellow-brown to green, then to 

 blue, violet, purple, red, and dirty yellow, in succession. 



Bile has no digestive action upon starch or proteids. It 



