280 PHYSIOLOGY OF ALIMENTATION. 



tions of HEIDENHAIN, 1 REID, 2 and COHNHEIM. HEIDENHAIN 

 found that when a dog's own blood-serum is introduced into 

 its intestinal tract it is absorbed. REID removed the intestine 

 from rabbits at the height of digestion and found when this 

 is cut open and stretched between two isotonic sodium chlo- 

 ride solutions that the salt solution is pumped from the side 

 of the mucosa toward the serosa. COHNHEIM found that when 

 the alimentary tract is removed from certain marine animals 

 (Holothuria tubulosa), and this is rilled with 10 to 30 c.c. of 

 sea-water, and the whole is then suspended in sea-water, 

 that this moves from the alimentary tract out into the sur- 

 rounding water. In all these experiments we have no dif- 

 ferences in osmotic pressure, and at present we cannot say 

 what makes the liquids move. The death of the cells, or 

 certain poisons such as sodium fluoride, arsenic, or chloro- 

 form, do away with this transport of serum, sodium chloride 

 solution, or sea-water from the side of the mucous mem- 

 brane toward the serosa, and make the alimentary wall act 

 like an ordinary dead diffusion membrane. But it explains 

 nothing, of course, when we say that such a transport is 

 dependent upon the living activity of the cells. 



The predominant permeability of the intestinal tract in 

 one direction can be markedly influenced experimentally. 

 When a dextrose solution is introduced into a loop of small 

 intestine, it is absorbed. According to experiments carried 

 out by GERTRUDE MOORE and myself this same glucose solu- 

 tion when injected into the blood is not excreted into the 

 lumen of the intestine. This happens, however, as soon as 

 certain salts (such as sodium chloride) are injected along 

 with the sugar solution, presumably because these salts 

 modify this predominant permeability in one direction. The 

 intestine in consequence now excretes a substance which it 



1 HEIDENHAIN: PFLUGER'S Archiv, 1894, LVI, p. 579. 

 'REID: Phil. Trans. Royal Soc., 1900, CXCII, p. 231. Journal of 

 Physiol., 101, XXVI, p. 436. 



