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2. On Compound Sugars. Saccharose, maltose and lactose, the three 



compound sugars, are believed by most observers to be not only non- 

 absorbable, but also non-assimilable and therefore are required to 

 undergo some digestive change before they can be absorbed and assimi- 

 . lated. An extract of the intestinal mucous membrane or the intestinal 

 juice of the dog added to a solution of saccharose will cause it to com- 

 bine chemically with water after which a cleavage into dextrose and 

 levulose will take place, which together constitute invert sugar. The 

 enzyme to which this action is attributed has been termed invertase or 

 saccharase. Maltose undergoes a similar change. After its combina- 

 tion with water it undergoes a cleavage into two molecules of dextrose. 

 Lactose appears to be unaffected by the pure juice. As it is non-assimi- 

 lable it has been supposed to undergo conversion into dextrose and 

 galactose while passing through the epithelial cells of the intestinal mu- 

 cosa. In either case the transformation is brought about by two fer- 

 ments known respectively as maltase and lactase. 



3. On Trypsinogen. This zymogen when first discharged from the pan- 



creatic duct is inactive and incapable of effecting the necessary digestive 

 changes in the proteins. Shortly after its entrance into the intestine, it 

 becomes quite active and efficient, a change attributed to an agent 

 entero-kinase secreted by the mucosa in the upper part of the intestine. 



THE LIVER 



The Liver. This highly vascular conglomerate gland is situated in the 

 right hypochondriac region and connected with the intestine by a duct. 



Inasmuch as the liver performs several functions related to both secretion 

 and excretion, a consideration of its structure and its various functions will 

 be deferred to a subsequent chapter. In this connection only the bile, its 

 physical properties, chemic composition, and physiologic action in relation 

 to the digestive process, will be considered. This fluid is a product of the 

 secretor activity of the liver cells. As it is poured into the intestine in man 

 and most mammals at a point corresponding to the orifice of the pancreatic 

 duct, and most abundantly at the time the food is passing through the duo- 

 denum, it is usually regarded as a digestive fluid possessing an influence 

 favorable if not necessary to the completion of the general digestive process. 



Anatomic Relations of the Biliary Passages. After its forma- 

 tion by the liver cells the bile is conveyed from the liver by the bile capillaries, 

 which unite finally to form the main hepatic duct. This duct emerges 

 from the liver at the transverse fissure. At a distance of about 5 centimeters 

 it is joined by the cystic duct, the distal extremity of which expands into a 

 pear-shaped reservoir, the gall-bladder in which the bile is temporarily 

 stored. The duct formed by the union of the hepatic and cystic ducts, the 

 common bile-duct, passes downward and forward for a distance of about 

 7 centimeters, pierces the walls of the intestine and passes obliquely through 

 its coats for about a centimeter and opens into a small receptacle, the ampulla 

 of Vater. The ampulla in turn opens on a small papilla into the intestine. 

 The walls of the biliary passages are composed of a mucous membrane 

 internally, a fibrous and muscular coat externally. The termination of the 

 common bile-duct is provided with a distinct band of circularly disposed 



