500 PROCEEDINGS OF THE AMERICAN ACADEMY. 



anced pressures, and the results, as shown by division, are better. This 

 is especially true if the normal relative proportions of the salts applied 

 be preserved, as the four-salt medium probably does approximately. 

 Changes in water-content within the limits here employed are not of 

 essential or even perceptible influence upon metabolism. That under the 

 prevailing conditions this factor is not important for our reckoning 

 appears from a consideration of its ineffective magnitude at the extremes 

 of the concentration curve. Stentors in distilled water did not suffer 

 from excessive inward osmosis of water, nor did Stentors near the oppo- 

 site extreme in milk sugar of hyperisotonic concentration suffer from 

 excessive abstraction of water. If the movement of water at either ex- 

 treme did not occur in sufficient intensity to prove harmful physiologically, 

 such effect may of course be excluded from the intermediate ranges. 



"We may now attempt to describe in summary the physico-chemical 

 processes for all concentrations of physiological salts. The form of the 

 general curve obtained from the results expressing division-reactions 

 shows a range of elevation more or less broad for medium concentrations, 

 with depressions on either side which reach zero at extremely high or 

 extremely low concentrations. At extremely high osmotic concentra- 

 tion of an indifferent substance (milk sugar) the destructive process is 

 abstraction of water. At extremely low concentration (distilled water) 

 the efficient factor in the harmful result is abstraction of physiological 

 salts. For intermediate concentrations the osmotic introduction or ab- 

 straction of water, as the case may be, is a factor necessarily present, but 

 of insufficient intensity to produce a disturbing physiological effect. Nor 

 does simple osmotic redistribution of salts, that is, physical alteration of 

 pressures of osrnotically active particles, account for the result. At equal 

 osmotic pressures, as curves previously given show, effects differ accord- 

 ing: to the individual salt. In the intermediate range of the concentration 

 curve alteration of constitutive proportion is the factor of primary efficiency. 

 It is worth while to notice that, owing to unbalanced partial pressures, 

 the phenomena in hypisotonic and hyperisotonic concentrations are essen- 

 tially similar processes. These consist in equilibration of pressures 

 leading to the same result, — the alteration of the normal constitutive 

 proportions of the physiological salts. Taking into account, then, the 

 whole range of the general curve, there may be distinguished three classes 

 of efficient factors. At one extreme there is (1) abstraction of water ; at 

 the other, (2) abstraction of all permeating salts, probably in the relative 

 proportion in which they are present in the organism ; and in the interme- 

 diate range, (3) alteration of constitutive proportion. Finally we must 



