72 PHYSICAL CHEMISTRY IN MEDICINE. 



in the partial dissociation into electrically charged ions 

 which salts, acids and bases suffer when dissolved in 

 certain solvents, especially water. 



The effects of salts within and without the organism 

 must all be treated from the standpoint of how far the 

 electrically charged ions or the electrically neutral mole- 

 cules play a part. Such an investigation, carried out 

 from both a theoretical and a practical point of view, is 

 to form the subject of my address to-day. 



L 



It is evident that there exist different ways in which 

 the unknown pharmacological properties of a substance 

 may be studied. As least practical and economical would 

 to-day be the attempt to employ the substance directly 

 in cases of illness. The animal experiment is little better, 

 and is of use only when it is possible to reproduce the 

 disease artificially in a more or less perfect way, as in 

 the case of the infectious diseases. Modern pharma- 

 cology has been very successful in predicting the nature 

 of the therapeutic effect of newly discovered chemical 

 compounds from their chemical constitution. There 

 exists, however, another way which, though still but 

 little used, renders it possible under suitable conditions 

 to discover unsuspected pharmacodynamic relations. 

 This is the application of a principle which I published 

 years ago, and which has since then rendered possible 

 the solution of difficult problems in physiology. This 

 may be called the principle of the manifold analogies 

 which exist between the changes in state suffered by colloids 

 and the changes that take place in living matter. In 



