FROM THE SMALL IiNTESTINE 639 



shown that the lung of a frog is much more permeable to C0 2 

 in the direction from pleura to bronchus, and that when the 

 lung is killed an excessive permeability still exists in the same 

 direction. These experiments, if true, certainly suggest that a 

 one-sided permeability in animal tissues may have a physical 

 or chemical basis. 



Hober s Experiments. Hamburger's work is not the sole evi- 

 dence that physical processes may play an important part in 

 intestinal absorption. Hober compared the rates of absorption 

 of a large variety of salts by Heidenhain's method. For this 

 purpose a known quantity of the solution is placed into an 

 intestinal loop of known length and ligatured at its two ends, 

 the loop is put back into the abdomen for a given time, and 

 at the end of the experiment the quantity of fluid in the gut 

 is measured. The A of the serum before the experiment, of 

 the original solution and of the fluid in the gut at the end of 

 the experiment is taken. He found, like previous observers, 

 that isotonic as well as anisotonic solutions were absorbed, and 

 that anisotonic solutions during absorption became more or less 

 isotonic with the animal's blood serum. In this way he inves- 

 tigated the absorption of many cations and of but few anions. 

 Wallace and Cushny observed by similar methods the absorption 

 of a great variety of anions and of but few cations. Their results 

 were identical with those of Hober when they overlapped, so that 

 the results of both series of experiments may be given together. 

 They show that both cations and anions differ enormously in 

 their rates of absorption. The various anions can be divided 

 into four groups with decreasing rates of absorption (1) chloride, 

 bromide, and iodide ; (2) nitrate, salicylate, &c. ; (3) sulphate, 

 phosphate, tartrate, citrate, &c. ; and (4) fluoride and oxalate. 

 The members of this last group injure the gut very materially. 

 The cations may be similarly divided into four groups (1) NH 3 , 

 together with urea ; (2) K, Na, Li ; (3) Ca, and (4) Mg. 



The cause of these great differences in absorption rate might 

 be vital or physical. Heidenhain had suggested that the different 

 rates of absorption of isotonic NaCl and MgS0 4 solutions was due 

 to the latter depressing the vital activity of the intestinal 

 epithelium by which the cells transported solutions from the gut 

 towards the blood-vessels. Such a vital explanation, however, 

 can be arrived at only by excluding every possible physical one. 



