446 ABSORPTION 



made to circumvent it by injecting the sugars parenterally i.e., into 

 subcutaneous or intramuscular connective tissue, into a serous sac, 

 or directly into the blood. Cane-sugar and lactose so introduced 

 are excreted unchanged in the urine. Dextrose, levulose, and 

 galactose are used up in the body, and some maltose likewise, 

 thanks to the presence of maltase in the blood and tissues. The cells 

 of the body in general wall burn only monosaccharides, and not di- or 

 poly-saccharides. Galactose and fructose are probably first con- 

 verted into dextrose before being utilized by the tissues, a change 

 which can also be readily induced in the test-tube. Therefore the 

 intestine admits the simple, but rejects the more complex sugars. 

 It is only in the presence of abnormally great quantities or ab- 

 normally great concentrations of the sugars which are not directly 

 utilizable that they are to a certain extent taken up unaltered, 

 to be for the most part quickly excreted as such (p. 540). In like 

 manner we have seen that the rtative proteins can, so to speak, 

 force their way by storm through the intestinal mucosa when 

 offered to it in exceptionally large amount. The sugar absorbed 

 from the intestine passes normally into the rootlets of the portal vein, 

 not into the chyle, for no increase in the quantity of that substance 

 in the contents of the thoracic duct takes place during digestion, 

 while the sugar in the portal blood is increased after a starchy meal. 

 The blood of the portal vein of a dog in the fasting condition con- 

 tained 0-2 per cent, of dextrose. During absorption of a meal rich 

 in carbo-hydrates it contained as much as 0-4 per cent. In the 

 lymph issuing from the thoracic duct the amount was the same in 

 both conditions viz., 0-16 per cent. In a case of lymph (chyle) 

 fistula in a human being, where almost all the lymph from the 

 digestive tract escaped through the fistula, out of 100 grammes of 

 carbo-hydrate taken (50 grammes starch and 50 grammes sugar), 

 only gramme, or not I per cent, of the sugar corresponding to the 

 carbo-hydrates of the food, could be recovered in the chyle. But 

 when a large amount of a dilute solution of sugar is introduced into 

 the intestine, some of it is taken up by the lacteals. 



Absorption of Water and Salts. The main channel for absorption 

 of these is the bloodvessels of the intestine. As much as 3 to 5 litres 

 of water can be absorbed in a day in the intestine of a healthy man, 

 exceptionally even 6 to 10 litres, without the faeces altering their 

 normal consistence. Absorption of the water and dissolved salts 

 may theoretically take place either through the epithelial cells (intra- 

 epithelial absorption), or between the cells (interepithelial absorp- 

 tion). According to Hober, most metallic salts (silver, mercury, 

 lead, bismuth, copper, manganese, etc.) are absorbed interepitheli- 

 ally, while iron salts form an exception, and pass into the epithelial 

 cells. The distinction between interepithelial and intra-epithelial 

 absorption does not rest upon an absolutely sure foundation. Yet 



