106 The Structure of Protoplasm 



sol. In a coacervate, according to Bungenberg de Jong, the col- 

 loidal units are attracted by electrostatic force but kept apart by 

 that of solvation. Thus the aggregrate, while coherent, may be 

 quite fluid. The whole cell has been compared by de Jong to a 

 compound mixed coacervate, but as already pointed out the liquid 

 endoplasm has normally the property of a sol. On the other hand, 

 so-called emulsion structure when it appears in cytoplasm may 

 well be a coacervation phenomenon, and reversible coacervation 

 (droplet precipitation) of colloids in the vacuole is a common oc- 

 currence. Compared with this the whole substance of a surface 

 film is suggested to be an irreversible coacervate mass having a 

 very low surface tension. 



Of the types of coacervate which have so far been studied ex- 

 tensively by Bungenberg de Jong, those which most resemble the 

 protoplasmic films are the auto-coacervates of phosphatides. Among 

 the points of resemblance are: 



relative irreversibility, due apparently to the formation of a 

 stable layer of orientated molecules at their surface; 

 lipophilic adhesion, due apparently to the hydrocarbon 

 chains of the orientated superficial molecules being directed 

 outward; 



myelin forvnation under certain conditions; 

 vacuole formation as a result of reduced colloidal hydration 

 (shared by other coacervates) along with nonfusion of the 

 vacuoles when pressed together, due apparently to separa- 

 tion by a very stable bimolecular film; and 

 change from optical isotropy to anistropy with dehydration. 

 There is also fair agreement between the action of electrolytes 

 on the packing of phosphatide films and on cell permeability, re- 

 spectively. On the other hand, their effect on electrophoresis of 

 cells is unlike that of phosphatide drops, inasmuch as the sign of 

 the charge at the cell surface is not so easily reversed. Perhaps 

 further study of coacervates which contain proteins as well as 

 lipoids may furnish still better models of the protoplasmic surface 

 film. 



In conclusion, let me point out the moral which my story is 

 meant to teach. It is the fallacy of taking a partial view to be a 

 true picture of the whole. That was the error of the blind men of 

 Indostan in their theorising on the structure of the elephant. I 

 cannot do better than parody this clever fable to suit the present 



