CHEMICAL CONSTITUTION AND PHARMACOLOGICAL ACTION. 437 



selective action. For a large number of substances which localize 

 in fat or fat-like bodies during life, it will probably be difficult to prove 

 whether a pure shaking-out process occurs or a formation of but 

 slightly soluble salts. 



Furthermore, both processes may occur toegther, as Knecht as- 

 sumes in dyeing, the lake-forming components being contained in 

 the tissues in the intimate molecular mixture characteristic of solid 

 solutions. In that case the resulting selective action will be due 

 to a combination of salt formation and solid solution. In many 

 instances, however, it will be extremely difficult to decide whether 

 one is dealing with solid solution or salt or double-salt formation, 

 especially since chemistry often finds it impossible to decide this 

 question in the case of pure bodies. This is seen, for example, in the 

 study of mixed crystals which are looked upon mostly as crystalline 

 solutions. 1 



In any case we see that even without the intervention of a chemic- 

 synthetic union the conditions necessary for a selective storage of a 

 substance in the organism are present and are sufficient both in 

 extent and in variety. 2 That these conditions in the case of the 

 salt-like combinations are essentially chemical in nature is self-evident; 

 in the case of the solid solution the enormous mass of evidence which 

 I have merely touched makes this extremely probable. If we regard 

 the principles governing distribution in the organism from these 

 standpoints we shall no longer be surprised that in the localization 



1 If two combinations of somewhat similar chemical constitution (for ex- 

 ample, benzole and pyridin; stilben, benzylidenanilin, and azobenzole; fluoren 

 and diphenylenoxid) form mixed crystals with each other, one can readily 

 comprehend this in view of their close chemical relationship, and can ascribe 

 it to "isomorphogenous" groups. Frequently, however, substances crystallize 

 together which exhibit the greatest divergence in the configuration of their 

 molecules, as, for example, phenol and urea, chloroform and salicylid, triphenyl- 

 methan and benzol. The crystalline fiery-colored combinations which picric 

 acid is able to effect with a large number of hydrocarbons are especially im- 

 portant. Certain investigations concerning the basic properties of oxygen 

 (Baeyer) and of carbon (Kehrman and Baeyer) seem to show that such crys- 

 tallizations, as, for instance, of ferrohydrocyanic acid with ether, etc., are anal- 

 ogous of salt formation. 



2 1 must here refer the reader to the extremely interesting investigations 

 of Spiro (Uber physikalische und physiologische Selection, Habilitationsschrift, 

 Strassburg 1897). In these, although starting from entirely different stand- 

 points *he author reaches many of the views held by me. At the time of my 

 address I was unaware of this study, as it is not to be had in the bookshops. 



