126 PROTOPLASMIC ACTION AND NERVOUS ACTION 



barrier is formed at any free surface of living protoplasm/ 

 This property of forming fresh semi-permeable surface 

 films at exposed protoplasmic surfaces has long been 

 known. NageH^ describes experiments with the root 

 hairs of Hydrocharis; by crushing these structures 

 under a cover-glass the protoplasm may be expressed in 

 the form of separate rounded vacuolated masses. Each 

 of these shows the same osmotic properties as the original 

 entire protoplast; i.e., shrinks in hypertonic solutions, 

 resists the entrance of dyes (during the living state), 

 and in general behaves as if it were surrounded with a 

 semi-permeable membrane. Such an experiment might 

 also be regarded as indicating the impermeability of all 

 parts of the protoplast to dissolved substances. But it 

 can be simulated by the simple experiment of breaking 

 or cutting up a large drop of an insoluble liquid, such as 

 chloroform, in a protein-containing medium; each result- 

 ing droplet remains separate and exhibits the same 

 properties as the original droplet, and the effect can be 

 shown to depend on the rapid formation of a thin protein 

 adsorption-film at the surface of each newly formed 

 droplet. In a somewhat similar manner, although the 

 conditions are more complex, Hving protoplasm forms 

 films at surfaces which are freshly exposed by cutting 

 or other injury; this property is shown only during life 

 and is presumably a manifestation of the normal property 

 of construction and repair, which is dependent on meta- 

 bolic synthesis, as we have seen. This is indicated by an 

 experiment of Pfeffer's,^ in which root hairs are placed in 



^ Cf. Chambers, Jour. Gen. Physiol., V (1922), 189. 

 ^Nageli, Pjlanzenphysiologische Studien, Zurich (1885). 

 ^Osmotische Untersuchungen (1877), p. 136. 



