ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 283 



fruits, and in the commercial " glucoses" (corn-sugar, molas- 

 ses, etc.). The dextrose and la?Yulose found in the alimentary 

 tract is derived, with the exceptions indicated, from the de- 

 composition of the polysaccharides and disaccharides of the 

 diet. Galactose enters as such into the diet practically not at 

 all. It is produced in the alimentary tract through the action 

 of lactase upon milk-sugar. Either directly or indirectly dex- 

 trose becomes the predominating sugar of the alimentary 

 tract. Not only does it constitute the bulk of the com- 

 mercial "glucose," but it, appears as the ultimate product of 

 the decomposition of every polysaccharide and disaccharide. 

 Glycogen is split directly into dextrose through amylase. The 

 same ferment converts starch into maltose, which through 

 maltase is converted into dextrose. Dextrose appears as one* 

 half of the product of the action of sucrase on sucrose, and 

 lactase on lactose. Cellulose, though acted upon only by the 

 bacterial enzymes of the alimentary tract, yields dextrose 

 when this occurs. 



We have to ask now in what form the carbohydrates of 

 the diet are absorbed. There seems to be little doubt that 

 the monosaccharides are absorbed as such. With the disac- 

 charides matters are somewhat different. If sucrose, maltose, 

 or lactose are fed slowly, they are all converted into mono- 

 saccharides before they are absorbed. When, however, these 

 disaccharides are fed rapidly, then they are not all split 

 before they are absorbed, and sucrose, maltose, and lactose 

 may be recovered as such from the blood and from the urine, 

 for these disaccharides when present in the circulating blood 

 in a concentration exceeding a very small fraction of a per- 

 cent are eliminated through the kidneys. Ordinarily it is 

 said that the disaccharides appear in the blood and the urine 

 if they are fed in too large amounts. This is not the essential 

 factor, however, ~but the time taken in feeding the amount, 

 for if the sugar solution is not absorbed too rapidly it does 

 not pass over into the blood in an unchanged state. 



Starch, glycogen, and cellulose all being colloidal bodies are 



