DIGESTION IN THE INTESTINE 147 



of hemoglobin of the blood. In their constitution they closely 

 resemble other known derivatives of hemoglobin. They contain 

 no iron. There has been much discussion as to where the trans- 

 formation of hemoglobin into bile pigments takes place. It is 

 probably in the phagocytic cells of the liver, which are believed 

 to engulf the red corpuscles and destroy them. The liver cells 

 then finish the transformation. 



Bile Salts. The bile salts, which are largely responsible for 

 the favorable action of bile in digestion and absorption of fats, 

 are mainly salts of glycocholic and taurocholic acids, two con- 

 jugated acids made up of cholic acid and glycocoll or taurine 

 respectively. Cholic acid is a complex substance of which the 

 formula is still uncertain. It is a specific product of liver cells 

 and is formed nowhere else in the body. Bile salts if mixed with 

 a little sugar and brought into contact with concentrated 

 sulphuric acid give a violet color. This is known as Petten- 

 kofer's test for bile salts. 



Bile contains small amounts of sodium soaps of various acids. 

 Bile from the bladder also contains a mucinous substance which 

 is perhaps largely a phosphoprotein. The nature of this sub- 

 stance is not definitely known. 



At times concretions known as "gall stones" form in the gall 

 bladder. They are composed of cholesterol, inorganic material 

 or bile pigment deposited from the bile. 



Intestinal Secretion 



The third of the important digestive fluids poured into the 

 intestine is called the intestinal juice or succus entericus. 

 The juice secreted into the duodenum is poured out by small 

 glands in the mucous membrane, the glands of Brun- 

 ner. Little is known of the mechanism by which these glands 

 are made to secrete. They are stimulated to activity when 

 the acid chyme passes the pylorus. The amount of juice secreted 

 has not been definitely determined, but it probably is large. The 

 juice is strongly alkaline, due to the presence of carbonates, and 



