340 SCIENCE PROGRESS. 



burger, or even the plasmolytic method of De Vries, but 

 is more applicable to coloured solutions, and is certainly 

 accurate enough for the gross differences dealt with in most 

 of the experiments. 



The osmotic pressure of serum is, of course, in the main 

 due to the relatively high partial pressure of the sodic 

 chloride which bulks as the main salt of the ash, for the 

 albuminous substances contribute but a small quota. 



That there is such a thing- as a physiological act of 

 absorption is again urged by Heidenhain, by showing that 

 if dog's serum of the same osmotic pressure as the serum 

 of the experimental dog is placed in the gut, its water and 

 salts are absorbed in the same ratio as they have in the 

 original fluid, so that the osmotic pressure of the residue in 

 the gut, if the absorption be interrupted, is little different 

 from that existing at the commencement of the experiment; 

 the albumin is absorbed more slowly than the salt, a tact 

 known long ago to C. Voit, but as mentioned above, the 

 albumin contributes but little to the total osmotic pressure 

 of the solution. In one case, serum with A^'Gi; 1 was 

 placed for two hours in the loop of the gut of a dog whose 

 serum had A= '626. At the end of this period, 42 per cent, 

 of the water and 40 per cent, of the salt had been absorbed, 

 and in the fluid remaining in the gut it was found that 

 A = '6oo. 



The same kind of absorption must also be possible for 

 solutions of sodic chloride of the same percentage as the 

 blood ; and it will be remembered that Gumilewsky had 

 shown this to be the fact, i.e., that with solutions in the 

 region of '6 to 7 per cent, the ratio of salt absorption to 

 water absorption is expressed by unity. Gumilewsky also 

 showed that with solutions of sodic chloride of higher per- 

 centage than the blood (since the salt passed into the blood 

 faster than the water), the ratio of salt to water absorption 

 is greater than unity ; while, on the other hand, with the 

 solutions of lower percentage than the blood, the water 



1 The symbol A is used to express the lowering of the freezing point 

 of a solution, and is proportional to its osmotic pressure. 



