PHASE REVERSAL IN EMULSIONS AND IN PROTOPLASM 127 



Regardless of the physical nature of the living colloidal particles, 

 there is no evidence upon which to base the assumption that a reversal 

 of phases takes place in protoplasm. Protoplasm is a lyophilic colloid. 

 Phase reversal was formerly thought to be the process by means of 

 which lyophilic colloidal sols, "emulsoid" sols, become gels (jellies). 

 The researches of Bachmann (1) and Zsigmondy (14), which have been 

 substantiated by a different method of investigation by McBain (10), 

 have shown that in gelatin (Bachmann) and soap (McBain) no reversal 

 of phases takes place in the transformation of the gelatin sol and the 

 soap sol into their gels. 



It is not my desire here to question further the emulsion theory of 

 protoplasmic structure. I do, however, wish to emphasize the fact that 

 the ideas that protoplasm is, in its colloidal nature, an emulsion, and that 

 this living emulsion is capable of phase reversal, are pure assumptions. 

 But we shall, with Clowes and others, tentatively assume that proto- 

 plasm is a colloidal emulsion in which a reversal of phases is a physical 

 possibility provided that the other prerequisite conditions, such as the 

 type of emulsifier, are favorable. It is with this last assumption, 

 namely, the type of emulsifier, that we are here primarily concerned. 

 That Clowes' hypothesis is highly interesting and that it opens up a new 

 line of speculation on the mechanism of permeability changes, goes with- 

 out saying. The question is, how far is the theory applicable? 



Acknowledgment. I had the pleasure of discussing the hypothesis 

 of Clowes with Mr. Hatschek of London. I objected to Clowes' 

 analogy on the grounds of the first two of the three assumptions named 

 above. Mr. Hatschek then called my attention to the third assumption, 

 namely, that if some emulsifier other than soap is used, the oil-in-water 

 emulsions will not reverse no matter how much salt of a bivalent cation 

 is added. This was demonstrated by a simple test-tube experiment in 

 which olive oil was emulsified in a weak aqueous solution of saponin. 

 An excess of BaCl 2 failed to cause a reversal. It was this demonstration 

 and subsequent discussion which ultimately led to the research work 

 here published. I wish not only to acknowledge the fact that the 

 original suggestion on which this article is based comes from Mr. 

 Hatschek, but I also desire to express my indebtedness to him for turn- 

 ing over to me the notes on his preliminary experiments. 



I wish also to make known my indebtedness to Prof. H. S. Uhler of 

 the Department of Physics of Yale University, who so kindly placed a 

 small laboratory and all necessary physical instruments at my disposal. 



Method. All of the emulsions worked upon were prepared by adding 

 25 cc. of oil to 25 cc. of an aqueous solution of the emulsifier. The mix- 

 ture was put into a 150 cc. flask and vigorously shaken intermittently. 

 This method of preparing an emulsion is that of Briggs (4), and con- 



