362 ABSORPTION 



unexplained factor bound up in the characteristics of the living protoplasm 

 of the epithelial cells themselves. When isotonic blood serum is introduced 

 into the intestine the salts and water are at once absorbed, also the albumins, 

 but more slowly. In this experiment the osmotic conditions are in balance 

 and the pressure is greater on the side of the blood-vessels, so that absorption 

 takes place with the actual expenditure of energy. The important fact 

 here is that the absorption through a living membrane is influenced by the 

 membrane in ways that we cannot yet explain. It is this factor which de- 

 termines the different rate of absorption and the so-called selective absorp- 

 tion in different regions of the alimentary canal. 



As a rule, the current of absorption is from the stomach or intestine into 

 the blood; but the reversed action may occur, as, for example, when sulphate 

 of magnesium is taken into the alimentary canal. In this case there is a 

 rapid discharge of water from the blood-vessels into the canal. The rapidity 

 with which matters may be absorbed and diffused through the textures of 

 the body has been found by experiment. It appears that lithium chloride 

 may be diffused into all the vascular textures of the body, and into some 

 of the non-vascular, as the cartilage of the hip joint, as well as into the aque- 

 ous humor of the eye, in a quarter of an hour after being given by way of the 

 mouth and on an empty stomach. Lithium carbonate, when taken in five- 

 or ten-grain doses on an empty stomach, may be detected in the urine in 

 five or ten minutes; or, if the stomach be full at the time of taking the dose, 

 in twenty minutes. 



Absorption in the Mouth. The epithelial lining of the mouth is 

 of the thicker stratified type and the conditions are otherwise unfavorable 

 for absorption. Little, if any, absorption normally takes place in the mouth, 

 and the same is true for the esophagus. 



Absorption in the Stomach. The mucous and sub mucous coats of 

 the stomach, see figure 258, are well supplied with blood-vessels and lym- 

 phatics. The mucous membrane is, however, so crowded with the peptic 

 glands that the relative amount of absorbing surface is small. It is limited 

 to the mucous membrane around the mouths of the glands. 



Recent experiments have shown that though absorption does take place 

 in the stomach, it is not as active as was formerly supposed, even in the case 

 of water. Von Mering has found that water begins to pass from the stomach 

 into the intestine almost as soon as it is swallowed, and that very little of it 

 is absorbed from the stomach. Of 500 c.c. given by the mouth to a large 

 dog with a duodenal fistula, only 5 c.c. were absorbed in 25 minutes, the 

 rest having passed into the intestine. Peptones, sugars, and salts are ab- 

 sorbed in the stomach, but only to a limited extent. Peptones are not ab- 

 sorbed in appreciable amount unless present to as much as 5 per cent or 

 more. Examination of the mucous membrane during the stage of active 

 digestion has revealed the presence of albumoses. Sugars, like peptones, are 



