468 THE HUMAN BODY. 



and not at all with iodine: they contain no glycogen and may 

 be compared with the cells of the pancreas in a late stage of 

 digestion (Chap. XIX). 



In the liver we have to deal with cells of twofold function; 

 the granular portion of each especially concerned with bile 

 secretion, and the larger portion of the cell with the making 

 of glycogen. In a salivary gland we have cells whose sole 

 apparent function is the formation of secretion to be poured 

 into the gland ducts; in the thyroid and suprarenal bodies 

 we find cells forming special materials which are passed into 

 blood or lymph. The hepatic cells do both, and it should be 

 borne in mind that possibly all gland-cells do. In fact it has 

 already been pointed out that the pancreas has still an- 

 other function than the formation of pancreatic juice. As 

 regards the liver-cells, we naturally ask whether the two 

 processes, bile-making and glycogen-rnaking, are distinct and 

 independent activities, or whether bile and glycogen are 

 simultaneous products of a single metabolic activity, as soap 

 and glycerine are of the chemical process of soap-making : 

 but to this question it is not possible yet to give a satisfactory 

 answer. 



The Source and Destination of Liver Glycogen. All 

 foods are not equally efficacious in keeping up the stock of 

 glycogen in the liver; fats by themselves are useless; proteids 

 by themselves give a little; by far the most is formed on 

 a diet rich in starch and sugar ; so it would seem tliat glyco- 

 gen is mainly formed from carbohydrate materials absorbed 

 from the alimentary canal and carried to the hepatic cells by 

 the portal vein. The chief of these materials is probably 

 glucose, since, although saliva and the amylolytic ferment of 

 the pancreas convert starch into maltose (C ia H M O n + H 2 0), 

 of the cane-sugar group, the intestinal secretion rapidly con- 

 verts this into grape-sugar or glucose. This is taken up by 

 the liver-cells, modified by them and stored as glycogen; and 

 by their further activity from time to time reconverted into 

 glucose and passed into the blood according to the needs of 

 the Body in general. The cells then do distinctly chemical 

 work on the carbohydrate material: possibly, indeed even 

 probably, they build that supplied into their own living sub- 

 stance and then by partial breaking down of this, deposit some 

 of it for a time as glycogen: and by further living activity 

 turn this into glucose and send it on to the blood, when the 



