1028 ABSORPTION 



quantities of water give rise to mechanical reflexes, nausea, irritations 

 of the gastric and intestinal mucosa, and certain symptoms associated 

 with hydremic plethora. 



One of the reasons for the relative ease with which the system may 

 be surcharged with water is that the alimentary surface is not suffi- 

 ciently resistant to counteract and to prevent osmosis. Moreover, 

 while the excessive intake of water may eventually cause the feces 

 in the large intestine to become watery, this channel offers a certain 

 resistance to its escape which it avoids by passing through the epithe- 

 lium . At least, this is the tendency in most persons. Thus, it is a matter 

 of common experience that constipation is usually associated with a 

 disinclination to take much water, and as much as 3 to 5 liters may be 

 absorbed, before the feces actually assume a fluid consistency. The 

 absorption of water is most intense in the small intestine, but some of 

 it also passes over into the cecum, because in this segment the fluid 

 ileac contents are gradually changed into the semi-solid feces. Under 

 normal conditions the stomach does not allow an appreciable quantity 

 of water to pass through, although slight amounts of peptones, sugar, 

 and certain drugs may be absorbed from its cavity. 1 It is for this 

 reason that stenosis of the pylorus and dilatation of the stomach are 

 usually accompanied by tissue-thirst, which cannot be relieved by 

 drinking. As far as the channel of absorption is concerned, it has 

 been observed that the introduction of salt solutions into the small 

 intestine does not increase the flow of lymph from the thoracic duct, 

 whereas large quantities of water frequently bring about a dilution 

 of the portal blood. It is probable, therefore, that these foodstuffs 

 pass directly into the blood-stream and not into the lacteals and lym- 

 phatic system. 



The osmotic interchanges between the intestinal contents and the 

 blood, may be illustrated in the following manner. A section of the 

 small intestine of an etherized mammal is drawn through a wound in 

 the abdominal wall. Two loops of equal size are then marked off 

 by three ligatures. Into one of these a quantity of normal saline 

 solution is injected which thoroughly distends its walls. Into the 

 other, a few drops of a concentrated solution of magnesium sulphate 

 are injected. Having replaced these loops in their proper place in 

 the abdominal cavity, the animal is allowed to rest for about one hour. 

 At the end of this time, it will be found that the loop containing the 

 saline solution, is now practically empty, while the formerly perfectly 

 flabby loop containing the magnesium sulphate, is highly distended. 

 This experiment clearly shows that the saline solution acts as a hypo- 

 tonic solution, and the magnesium sulphate solution as a hypertonic 

 solution. In the former case, water is removed from the intestinal 

 canal, and in the latter, from the blood. This is the picture of saline 

 catharsis, because the introduction of such solutions as citrate of mag- 



1 Moritz, Zeitschr. fur Biol., xlii, 1901, 565. 



