1915] 



CZAPEK — PROTOPLASM AND ITS COLLOIDAL PROPERTIES 245 



The chemistry of colloids is not a descriptive science. To 

 the utmost extent it has to use experimental physical methods. 

 So we cannot advance in knowledge of protoplasm by mere 

 microscopical observation, but mainly by experimental investi- 

 gation. 



A long time even before colloidal chemistry became domin- 

 ant as the basis for the physiology of protoplasm, a memorable 

 epoch in plant physiology had opened, developing from the 

 ingenious work of Pfeffer and De Vries on the osmotic prop- 

 erties of living cells. These investigations unveiled the 

 fundamental fact that living protoplasm alone is in posses- 

 sion of those peculiar properties of permeability which are 

 responsible for the whole complex of nutrition. Dead proto- 

 plasm behaves quite differently. Since, however, differences 

 in respect of the penetration of different solutions can be 

 detected to a certain extent in colloidal membranes, it be- 

 came probable that the so-called semipermeability of living 

 protoplasm is a colloidal phenomenon, due to the constituent 

 colloids in living protoplasm; whilst after the death of the 

 cells the coagulation of these colloids completely changes the 

 peculiar permeability of the protoplasmic layer. 



It was, however, Ernest Overton, in 1899, then at Zurich, 

 who acquired the merit of placing colloidal chemistry in 

 fundamental relation to the phenomena of diosmosis in living 

 cells. The well-known theory of Overton consists in the 

 hypothesis that fatty substances play an important role as 

 constituent elements in the protoplasmic matrix. It is due to 

 such substances, generally comprised under "lipoid bodies," 

 that living cells show quite distinctive diosmotic qualities. 

 Overton's hypothesis is founded upon the fact that only those 

 substances which readily dissolve in fatty oils are easily diffus- 

 ible in living cells; whilst all substances which are insoluble 

 in oily media, as sugar or mineral salts, easily produce plas- 

 molysis, because they penetrate into cells only very slowly. 



The leading physical idea in this theory was the so-called 

 "Partition-Rule" of Berthelot and Jungfleisch. This law 

 states the fact that there exists a constant relation between 

 the Quantities of a certain solute dissolved in two immiscible 



