CHEMICAL PHENOMENA IN LIFE 



enough to affect the superficial layer of proto- 

 plasm. So lecithin or cholesterin emulsions 

 are quite as effective as true surface-active solu- 

 tions. But emulsions of neutral fats never produce 

 toxic effects. The determination of the amount of 

 surface tension in emulsions of neutral fats as 

 highly concentrated as possible, gave the result 

 that such emulsions regularly depress the surface 

 tension to two-thirds of the value of that of pure 

 water. Since fatty compounds are always present 

 in protoplasm, it does not seem to be by chance 

 that the surface tension of living protoplasm 

 and the surface tension of fat emulsions are 

 practically the same. The conclusion may 

 perhaps therefore be drawn that the superficial 

 layer of protoplasm contains an emulsion of neutral 

 glycerids, such as triolein, linolein, ricinolein, and 

 others. 



Overton's and Quincke's theory that the peri- 

 pheral layer of protoplasm can be compared to an 

 oily film or a very thin layer of fat (Overton 

 thought of lecithin or cholesterin) does not seem 

 to be quite a correct one. The ordinary food of 

 plants consists of watery solutions of substances 

 which are usually not soluble in fat. It is, as I 

 think, more probable that the fat in the plasmatic 

 membrane is present in the form of an emulsion 

 of extreme fineness. The interstitial space 

 between the fat-globules must be filled up with a 

 watery colloid solution, most probably a protein 



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