ABSORPTION 417 



not di- or poly-saccharides. Therefore the intestine admits the 

 simple, but rejects the more complex sugars. It is only in the 

 presence of abnormally great quantities or abnormally great 

 concentrations of the sugars which are not directly utilizable 

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

 quickly excreted as such (p. 516). 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 con- 

 dition contained o - 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 J gramme, or not i per cent, of the sugar 

 corresponding to the carbo-hydrates of the food, could be re- 

 covered 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 absorp- 

 tion 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 absorption). According to Hober, most 

 metallic salts (silver, mercury, lead, bismuth, copper, manganese, 

 etc.) are absorbed interepithelially, 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 it is probable that 

 everything which is useful in the nutrition of the body is taken 

 up by the cells, while such substances as metallic salts which 

 are foreign to the organism, and are denied entrance into the 

 cells, may pass in small amount between them, their passage 

 being perhaps associated with more or less injury to the inter- 

 stitial substance. The vigilant selection exercised by the 

 mucosa is well illustrated by the facts that, although manganese 

 and iron are chemically so closely related, iron, which is necessary 

 for the formation of the blood-pigment, is absorbed in immensely 

 greater amount than manganese; and that chlorides, especially 



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