344 SCIENCE PROGRESS. 



The result is not due to any raising of the total osmotic 

 pressure of the solution in the gut by the addition of the 

 small amounts of sodic fluoride. The result of raisino- the 

 total osmotic pressure of a " weak " solution of sodic 

 chloride in the gut by adding, say, sodic sulphate, is that 

 the passage of water out of the gut is diminished, and 

 though by deleterious action on the active-cells the output 

 of sodic chloride might also be affected, the effect upon the 

 water stream must be predominant. Experiment substan- 

 tiates this, i.e., an exactly opposite result to that got with 

 the fluoride. Moreover, the action of sodic sulphate is only 

 manifest when it is actually present in the gut, while, as 

 seen above, that of fluoride lasts some time after its 

 removal. 



Finally, Heidenhain gives the case of two isotonic solu- 

 tions of different salts placed in the gut. If water is 

 absorbed at all from such solutions, it should, on the purely 

 physical theory, be absorbed at the same rate in each case. 

 But water is absorbed far more quickly from a sodic 

 chloride solution than from an isotonic solution of magne- 

 sium sulphate ; indeed, a sodic chloride solution whose 

 osmotic pressure exceeds that of the blood loses water 

 quicker than a magnesium sulphate solution whose osmotic 

 pressure is below that of the blood, and the higher "osmotic 

 equivalent " of the magnesium sulphate is not worth reckon- 

 ing with in such conditions, for the total amount of the salt 

 entering the blood is so small, that its "equivalent' 1 of 

 water entering the gut is but a minute fraction of the large 

 amount of water actually absorbed. 



We have referred to this last paper of Professor 

 Heidenhain's at some length, since it represents the results 

 of work that has been going on at Breslau for some years, 

 and the opinion of one highly qualified to treat the subject. 

 It must, however, here be noted that the interference with 

 an artificially set up osmotic stream by the use of a physio- 

 logical depressant, is not here demonstrated for the first 

 time. The effect was demonstrated, now four years back, 

 by Waymouth Reid, who, in the absorbing skin of the frog, 

 showed not only that chloroform diminished a stream of 



