1915] 



CZAPEK PROTOPLASM AND ITS COLLOIDAL PROPERTIES 247 



sorption into living protoplasm. According to the theorem 

 of Willard Gibbs the surface in liquid systems which consist 

 of different fluids and contain some capillary-active sub- 

 stances is always occupied by those substances which show 

 the greatest reduction in the surface tension of the medium. 

 If subsequently another substance with greater capillary 

 activity is added to the system it displaces all other substances 

 from the surface. Narcotics may displace certain plasmic 

 substances in an analogous way, provided that the surface 

 tension of the concentration applied is just a little lower than 

 the surface tension of the plasmatic substances referred to. 

 The fact that the fatal narcotic pressure value coincides with 

 the maximum surface tension in fat emulsions may be ex- 

 plained by the hypothesis that fatal effects of alcohols on 

 living cells consist in destroying the emulsion structure of 

 protoplasm, by displacing some fatty substances. So our 

 experiments to a certain extent uphold the view that the 

 surface layer of protoplasm really contains fat, and thus far 

 is in accordance with Overton's hypothesis. 



In the course of time the lipoid-theory of Overton has met 

 with sharp criticism. Among other renowned physiologists, 

 Ruhland strongly denied the presence of fatty bodies in the 

 plasmatic membrane of plant cells. On the other hand, we 

 are aware that animal physiologists, such as Fiihner, Hober, 

 and Vernon still firmly adhere to the old lipoid-theory. 

 However, since according to Overton sugars and mineral 

 nutrient salts are believed to penetrate only poorly into the 

 living cell, it is obvious that Overton's hypothesis stands in 

 direct contrast to the common experiences in respect to plant 

 nutrition. The substances referred to are materials which 

 the cells have to take up as among their most important 

 nutrients. Nevertheless, there have been developed some sup- 

 plementary theories which permit us to lessen the difficulties 

 of the lipoid-theory, for example, that of Nathansohn, accord- 

 ing to which the lipoid membrane of protoplasm is not a con- 

 tinuous film of fat, but a kind of mosaic of fat and protein 

 which is able to permit the penetration of both fat-soluble 

 substances and mineral salts. 



