ADAPTATION TO ENVIRONMENT WARDLAW 401 



recognized by Kinger (1884). In his classical series of papers he 

 investigated in some detail the effect of variations of these propor- 

 tions on the properties of living matter. These investigations have 

 been the starting point of much of the later work. Hamburgher 

 (1921), who made use of a rather highly specialized type of cell 

 for his experiments, was the first to study directly this effect on the 

 permeability of the cell wall. He was able to demonstrate clearly 

 that variations of the proportions of the ions in the fluid to 

 which these cells were exposed were able markedly to alter their 

 permeability towards different materials. 



Comparative studies have not so far been made to show how the 

 power of the organism to regulate the relative proportions of the 

 different elements, or more particularly ions, in its substance has 

 developed during the course of evolution. A great deal of attention 

 has been paid within recent years to the study of the proportions be- 

 tween the hydrogen and hj^droxyl ions which are derived from the 

 medium in which all the vital reactions take place. It seems, how- 

 ever, that the power of regulating the proportion between these ions 

 must be of later development than the ability to preserve certain 

 ratios between various other ions. Among the lower organisms con- 

 siderable variation of the concentration of hydrogen ions may be sur- 

 vived by some forms. In the highest forms of life, however, the con- 

 centration of those ions is kept extraordinarily constant. It is al- 

 lowed to vary between narrower limits even than the osmotic pres- 

 sure. The proportions between certain inorganic substances in solu- 

 tions, such as those in the neighborhood of and within living cells, 

 determine what shall be the proportions between the ions of the sol- 

 vent water. Indeed, even in the higher organisms, the occurrence of 

 rapid variations in the proportions of these ions is prevented by the 

 concentrations of certain other substances which are present. These 

 are known as buffer substances. Among the inorganic salts which 

 exercise this controlling action the more important are the sodium 

 salts of carbonic and phosphoric acids. 



The control of the permeability of the living cells must thus largely 

 depend on the composition of the medium with which they are in con- 

 tact, and on the presence of certain substances in the cells themselves. 



The mechanism controlling the total concentration or osmotic pres- 

 sure of the medium bathing the cells of an organism, on the other 

 hand, must also be actuated by the composition of this medium, but 

 in a manner different from that by which it influences the permea- 

 bility of the tissues. It is true that the exchange of material between 

 an organism with a closed circulatory system and its environment is 

 limited to certain areas of its surface, for example, to the areas 

 covered by the epithelium of the alimentary and respiratory tracts. 



