THE ABDOMEN. 151 



the manufacture of the bile pigments, bilirubin and bili- 

 verdin, which are made from the hemoglobin of the 

 blood, seems to require some special action on the part of 

 the liver cells. 



The glycogen, which is manufactured and stored in the 

 liver cells, is a clear hyaline substance, akin to starch and 

 capable of being converted into sugar by the starch fer- 

 ment. Probably there is some such ferment in the blood 

 which converts the glycogen into sugar as soon as it passes 

 from the liver into the blood, though what it is, is not 

 known. Neither is it known just how glycogen is formed, 

 but it is manufactured chiefly after a mixed meal in which 

 carbohydrates predominate, proteins having little and 

 fats no effect upon its formation. It is undoubtedly 

 formed from the sugar in the portal blood and the pro- 

 cess requires some work on the part of the liver cell itself. 

 Probably there is always some sugar in the circulating 

 blood which, as it is used up, must be made good. If 

 there it not enough in the diet, the liver supplies the 

 deficiency from its store of glycogen. 



Glycogen is found also in the muscles, in the placenta 

 as food for the fetus, in leucocytes, and to a slight extent 

 in cartilage. In fact, it is the form in which carbohydrate 

 material is supplied to the tissues as needed. Normally, 

 much of the sugar is used up by the blood and its cells in 

 metabolism, giving rise to heat and energy. In muscles 

 glycogen is probably digested as lactic acid, as before 

 action muscle is neutral or slightly alkaline and after 

 action acid. 



When the liver is deranged and allows the glycogen to 

 pass out into the blood too freely, or when the glycogen is 

 not held as such but turned to sugar and passed out in 

 large quantities, sugar in the urine or diabetes mellitus 

 results. 



Besides its secreting function the liver has an elimina- 

 tive function and plays an important part in purifying the 

 blood, removing from it many poisonous and narcotic 

 substances. It is thought by some, though it has not 



