316 FUNCTIONS OF NUTRITION. 



with various saline solutions, were immersed in reservoirs of pure 

 water, so that the level of the water in the reservoir was a little 

 higher than that of the solution in the interior vessel ; and after they 

 had been allowed to remain for a time at rest, at a constant tempera- 

 ture, the quantity of solution which had escaped into the surrounding 

 liquid indicated the rapidity with which diffusion had taken place. By 

 this method it was found that the diffusibility of different liquids varies 

 in an analogous way with their absorption by animal tissues, and is 

 influenced by similar conditions. Solutions of different salts, in the 

 same degree of concentration, are diffused with different degrees of 

 rapidity ; and the same solution, other conditions remaining equal, 

 increases in diffusibility with the elevation of temperature. The fol- 

 lowing table shows the comparative diffusibility of various saline 

 solutions in pure water at different temperatures : 



DIFFUSIBILITY OF SALINE SOLUTIONS IN PURE WATER. 



At 3 C. At 15.3 C. 



Sodium chloride .... 22.47 . . . 32.25 



Sodium nitrate .... 22.79 . . . 30.70 



Ammonium chloride . . . 31.14 . . . 40.20 



Potassium nitrate . . . 28.70 . . . 35.55 



Potassium iodide . . . .28.10 . . . 37.00 



Magnesium sulphate . . . 13.07 . . . 15.45 



The rapidity of diffusion is influenced, not only by temperature, but 

 also by the degree of concentration of the solution and by the chemi- 

 cal constitution of the salt which it contains. A concentrated solution 

 diffuses into pure water more rapidly than one which is comparatively 

 dilute ; and, if the solution be maintained at its original degree of con- 

 centration while the exterior liquid is replaced by pure water, diffusion 

 continues with greater energy than if the two liquids are allowed to 

 become changed by mutual admixture. Salts of potassium diffuse 

 more rapidly than the corresponding salts of sodium ; and in each 

 instance salts of the monobasic acids diffuse more rapidly than those 

 of bibasic acids with the same metals. Sugar, gum, and albumen 

 are less diffusible than the soluble mineral salts, and of all the 

 substances examined albumen is the least so, being diffused only 

 one-twentieth part as readily as sodium chloride. Urea, on the other 

 hand, is nearly as diffusible as sodium chloride If the interior vessel 

 contain a mixed solution of several substances, each is diffused with 

 its own specific rapidity, so that after a time they are found in the 

 water of the reservoir in different quantities. Various other peculiari- 

 ties are observed, showing the influence of the chemical character of a 

 salt upon its diffusibility. 



In the experiments of Hoppe-Seyler,* the influence of repose or agi- 

 tation on the rate of diffusion was fully demonstrated. Concentrated 

 solutions of sugar, albumen, or other substances having a rotatory 



* Physiologische Chemie. Berlin, 1877, p. 145. 



