PROTOPLASMIC STRUCTURE 105 



at the surfaces of cuts made with microdissection 

 needles, or around isolated portions of protoplasm.^ 



Apparently the nearest inorganic analogies to these 

 protoplasmic film-structures are the thin surface-films 

 deposited at the boundaries between mutually insoluble 

 liquids, one or other of which contains surface-active 

 (especially colloidal) materials in solution; good illus- 

 trations are the films of soap or other material surround- 

 ing the droplets in an oil-water or other emulsion, or the 

 solid films formed about globules of oil, mercury, chloro- 

 form, or other insoluble liquids immersed in protein- 

 containing solutions, or the haptogen membranes formed 

 at the surfaces of warm soap solution, milk, or solutions 

 of protein, peptone, saponin or other surface-active 

 colloidal substances. Under certain conditions these 

 films may acquire a solid consistency and exhibit con- 

 siderable structural density, and thus limit diffusion 

 between the two phases; the resulting system may then 

 be described as triphasic, the three phases being the 

 internal medium, the external medium, and the inter- 

 vening thin phase or membrane. The ''artificial cells" 

 described by Harvey,^ made by breaking up a chloroform 

 solution of lecithin in dilute egg-albumin, may be cited 

 as examples of structures formed under these conditions. 



In living protoplasm it is to be presumed that 

 condensation-films of protein and other surface-active 

 substances are formed at all of the surfaces bounding 



^ Chambers, American Journal of Physiology, XLIII (19 17), i; Pro- 

 ceedings of the Society of Experimental Biology and Medicine, XVII 

 (1919), 41; Jour. Gen. Physiol., V (1922), 189. For plant cells cf. 

 Prowazek, Biol. Zentr., XXVII (1907), 737. Drops of protoplasm 

 from Vaucheria form membranes about their surfaces. 



^ E. N. Harvey, Science, XXXVI (191 2), 564. 



