180 THE PROCESSES OF DIGESTION AND RESORPTION. 



maltase, and lactase, which are partly furnished by the pancreas, 

 but principally by the enteric juice. This inversion is likewise of 

 the nature of a hydrolytic process, and may be represented by the 

 general equation : 



C 12 H 22 O n + H 2 = 2C 6 H 1 ,0 6 

 Disaccharide. Mouosaccharide. 



To judge from certain experiments which have been performed 

 on animals, it appears that amylolysis can also take place in the ab- 

 sence of the principal gland by which the ptyalin is formed, viz., 

 the pancreas. For we find that following the extirpation of this 

 organ or ligation of the pancreatic duct dogs are still capable of 

 utilizing as much as from 47 to 71 per cent, of the starch ingested. 

 As the dog's saliva contains no ptyalin, the amylolysis cannot be 

 referable to a converting activity of the salivary glands. Whether 

 in such cases the small amount of ptyalin which is furnished by the 

 enteric juice is sufficient to transform the ingested starch into mal- 

 tose is questionable, and there is some reason for supposing that the 

 epithelial cells of the small intestine are capable not only of causing 

 the transformation of disaccharides to monosaccharides but also of 

 inverting dextrin to maltose. It has been shown that in animals 

 with Thiry-Vella fistulae injected solutions of starch and cane-sugar 

 rapidly disappear, although maltose cannot always be demonstrated 

 in the fluid. In what manner this change is effected by the epi- 

 thelial cells is not known. In any event it is necessary that the 

 polysaccharides should be inverted to monosaccharides before pass- 

 ing beyond the mucous membrane of the gastro-intestinal tract. 

 Resorption takes place primarily through the specific activity of the 

 epithelial lining of the intestinal rnucosa. /The monosaccharides 

 then enter the blood-current and are carried to the muscles and the 

 liver, where they are transformed into glycogen and stored in a 

 manner analogous to the reserve starch of the plant. This trans- 

 formation, however, as well as the subsequent fate of the sugar, we 

 shall have occasion to study in greater detail in a subsequent 

 chapter. 



Neither the polysaccharides nor the disaccharides when introduced 

 into the blood-current directly can be utilized by the body as such, 

 and they are accordingly eliminated in the urine as foreign matter. 



The extent to which amylolysis can occur in the intestinal canal 

 is remarkable, and far exceeds the ability of the liver and the 

 muscle-tissue to transform the corresponding amount of glucose into 

 glycogen. As a consequence, the percentage of circulating sugar 

 rises beyond the normal and glucosuria results (alimentary gluco- 

 suria). That disaccharides may pass the intestinal mucosa without 

 being inverted is possible, but certainly of exceptional occurrence. 

 In such cases we must imagine that the intestinal epithelium has 

 lost its specific power as a barrier to the passage of the sugars, as 

 well as its ability to cause their inversion. As a result they pass 



