PHASE REVERSAL IN EMULSIONS AND IN PROTOPLASM 137 



plasm an emulsifier that will permit reversal of phases in the living emul- 

 sion (assuming with Clowes that protoplasm is an emulsion) when the 

 salt or hydroxide of a mono- or bivalent cation is added? A brief review 

 of the foregoing experimental data is sufficient to show that an answer 

 to the question at hand is impossible. 



That protoplasm contains soaps we know, but their proportion, com- 

 pared with that of "lipoids" and proteins, is small. It seems unlikely that 

 soap is the emulsifier that is the determining one in the behavior of the 

 hypothetical protoplasmic emulsion. All experiments on permeability 

 tend to emphasize the presence of proteins and "lipoids" in the plasmatic 

 membrane. If the emulsifier active in protoplasm is a "lipoid," then the 

 question arises whether it is like lecithin, in which case reversal could 

 not happen, or like cholesterin in which case reversal could take place. 

 Lecithin is more abundant in plant tissue, and cholesterin in animal 

 tissue. Whether the "lipoid" is free and functions as such is doubtful. 

 Osborne (10) finds that of a maximum content of 30 per cent of "lipoid" 

 in egg yolk very little is free, the greater portion being chemically bound 

 with proteins. 



The abundance of proteins in protoplasm makes it highly probable 

 that the predominating emulsifier is a protein. But this does not sim- 

 plify our problem. If the emulsifier is an albumin then reversal is not 

 possible, while if it is casein or gliadin, or a protein behaving like them, 

 then reversal is possible. Who can say what the actual nature of the 

 substance is which keeps the supposed protoplasmic emulsion in a state 

 of equilibrium? 



Clowes' hypothesis suffers not only from the fact that emulsions with 

 certain kinds of emulsifiers will not reverse, but also from the fact that 

 those emulsions which do reverse do so on the addition of the hydroxide 

 but not the chloride of sodium. The fact that NaCl will not reverse 

 any of the emulsions is of importance in its bearing on the behavior of 

 protoplasm, because it is with NaCl that such pronounced changes in 

 protoplasmic permeability have been observed by many biologists. 



In view of the extremely slight if any tendency of NaCl to produce the 

 formation of water-in-oil emulsions, and especially, in view of the inabil- 

 ity of NaCl to reverse any of the emulsions here reported upon, it must 

 be evident that Clowes' hypothesis can not be considered to cover the 

 mechanism of the changes in protoplasmic permeability by sodium chlor- 

 ide at least. 



Clowes has given us some interesting suggestions. If it should be 

 found that protoplasm is, in its colloidal structure, an emulsion, and 

 that this emulsion is maintained by an emulsifier which permits a rever- 

 sal of the liquid phases making up the system, then and only then can 

 the speculations of Clowes serve as the foundation of a theory of the 



