338 SCIENCE PROGRESS. 



3. The total osmotic pressure of a mixture of dissolved 

 substances is equal to the sum of the partial pressures of 

 the several ingredients. 



4. If solutions of equal total osmotic pressures but un- 

 equal partial pressures of the dissolved substances are 

 separated by a porous membrane, any constituent of the 

 mixture passes from the side at which it is present at 

 higher partial pressure to the other side, until the partial 

 pressures on the two sides are in equilibrium. No passage 

 of water across the membrane, however, takes place. 



If intestinal absorption depends upon osmosis, the facts 

 of experiment must conform with the above laws. 



In 1885 a series of researches was commenced in the 

 Breslau laboratory under Heidenhain's direction with a 

 view to deciding the question. 



Leubuscher found that solutions at body temperature 

 supplied to a loop of gut in a narcotised dog were absorbed, 

 and better at a pressure of about 10 cm. of water than 

 above or below ; unfolding of the intestinal walls obviously 

 at low pressure favours absorption by exposing more 

 surface, while at high pressure compression of the blood- 

 vessels of the mucosa interferes. His most important 

 point was that "25 to "5 per cent, sodic chloride solutions 

 were absorbed quicker than water. At 2 per cent, up to 

 10 per cent, a clear osmotic process was evident, for while 

 the volume of fluid in the gut increased, the amount of 

 sodic chloride fell. With such strong solutions, however, 

 it is, of course, impossible to regard the condition of the 

 epithelium as normal. Comparing the absorption of sodic 

 and potassic chloride, it was found that the former is 

 absorbed faster than the latter, though Graham showed 

 that potash salts are the more diffusible of the two. 



Gumilewsky, using a dog with a Vella fistula, confirmed 

 Leubuscher's point regarding the fact that weak sodic 

 chloride solutions are absorbed with greater rapidity than 

 pure water, but added that the relative rates of absorption 

 of water and salt in sodic chloride solutions varies with the 

 concentration. 



At a strength of about '6 per cent., the salt and the 



