I04 PROTOPLASMIC ACTION AND NERVOUS ACTION 



and various impregnated types of membrane, in the 

 hope of throwing Hght upon the pecuHarities of living 

 membranes. The resemblance of these artificial struc- 

 tures with the protoplasmic membranes seems, however, 

 in many cases remote. The conditions observable in 

 living protoplasm indicate that membranes of a different 

 and somewhat special type, viz., the interfacial films 

 formed between the separate phases in emulsions and 

 other polyphasic systems, have a closer affinity with 

 protoplasmic membranes than any other simple t>"pe of 

 physical structure. 



The property of forming thin films at structural sur- 

 faces of all kinds is highly characteristic of living proto- 

 plasm. The entire cell body is separated from the 

 surrounding medium by the plasma membrane; within 

 the cell the nuclear area is sharply delimited by a mem- 

 brane which usually disappears only during mitosis; 

 structurally distinct membranes are also formed about 

 fibrils, vacuoles, alveoli, chromatophores, spheres, 

 chromosomes, and various cell-inclusions. Apparently 

 the conditions required for the formation of thin solid 

 films are present everyw^here in living protoplasm; at 

 any structurally well-defined surface, continuous sheets 

 of material may be deposited; the formation of mem- 

 branes at cut surfaces and about extruded portions of 

 protoplasm is simply one illustration of this general 

 property.^ The fertilized eggs of marine animals 

 (sea-urchin, starfish) are especially favorable objects 

 for showing this property; new films are rapidly formed 



^ For a recent account of these phenomena, see the review by Seifriz, 

 Annals of Botany, LXXXVIII (1921), 269; cf. also Botanical Gazette, 

 LXX (1920), 360. 



